pragma solidity ^0.5.5;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following 
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Converts an `address` into `address payable`. Note that this is
     * simply a type cast: the actual underlying value is not changed.
     *
     * _Available since v2.4.0._
     */
    function toPayable(address account) internal pure returns (address payable) {
        return address(uint160(account));
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     *
     * _Available since v2.4.0._
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-call-value
        (bool success, ) = recipient.call.value(amount)("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}

// SPDX-License-Identifier: Unlicense
/*
 * @title Solidity Bytes Arrays Utils
 * @author Gonçalo Sá <goncalo.sa@consensys.net>
 *
 * @dev Bytes tightly packed arrays utility library for ethereum contracts written in Solidity.
 *      The library lets you concatenate, slice and type cast bytes arrays both in memory and storage.
 */
pragma solidity >=0.5.0 <0.7.0;


library BytesLib {
    function concat(
        bytes memory _preBytes,
        bytes memory _postBytes
    )
        internal
        pure
        returns (bytes memory)
    {
        bytes memory tempBytes;

        assembly {
            // Get a location of some free memory and store it in tempBytes as
            // Solidity does for memory variables.
            tempBytes := mload(0x40)

            // Store the length of the first bytes array at the beginning of
            // the memory for tempBytes.
            let length := mload(_preBytes)
            mstore(tempBytes, length)

            // Maintain a memory counter for the current write location in the
            // temp bytes array by adding the 32 bytes for the array length to
            // the starting location.
            let mc := add(tempBytes, 0x20)
            // Stop copying when the memory counter reaches the length of the
            // first bytes array.
            let end := add(mc, length)

            for {
                // Initialize a copy counter to the start of the _preBytes data,
                // 32 bytes into its memory.
                let cc := add(_preBytes, 0x20)
            } lt(mc, end) {
                // Increase both counters by 32 bytes each iteration.
                mc := add(mc, 0x20)
                cc := add(cc, 0x20)
            } {
                // Write the _preBytes data into the tempBytes memory 32 bytes
                // at a time.
                mstore(mc, mload(cc))
            }

            // Add the length of _postBytes to the current length of tempBytes
            // and store it as the new length in the first 32 bytes of the
            // tempBytes memory.
            length := mload(_postBytes)
            mstore(tempBytes, add(length, mload(tempBytes)))

            // Move the memory counter back from a multiple of 0x20 to the
            // actual end of the _preBytes data.
            mc := end
            // Stop copying when the memory counter reaches the new combined
            // length of the arrays.
            end := add(mc, length)

            for {
                let cc := add(_postBytes, 0x20)
            } lt(mc, end) {
                mc := add(mc, 0x20)
                cc := add(cc, 0x20)
            } {
                mstore(mc, mload(cc))
            }

            // Update the free-memory pointer by padding our last write location
            // to 32 bytes: add 31 bytes to the end of tempBytes to move to the
            // next 32 byte block, then round down to the nearest multiple of
            // 32. If the sum of the length of the two arrays is zero then add
            // one before rounding down to leave a blank 32 bytes (the length block with 0).
            mstore(0x40, and(
              add(add(end, iszero(add(length, mload(_preBytes)))), 31),
              not(31) // Round down to the nearest 32 bytes.
            ))
        }

        return tempBytes;
    }

    function concatStorage(bytes storage _preBytes, bytes memory _postBytes) internal {
        assembly {
            // Read the first 32 bytes of _preBytes storage, which is the length
            // of the array. (We don't need to use the offset into the slot
            // because arrays use the entire slot.)
            let fslot := sload(_preBytes_slot)
            // Arrays of 31 bytes or less have an even value in their slot,
            // while longer arrays have an odd value. The actual length is
            // the slot divided by two for odd values, and the lowest order
            // byte divided by two for even values.
            // If the slot is even, bitwise and the slot with 255 and divide by
            // two to get the length. If the slot is odd, bitwise and the slot
            // with -1 and divide by two.
            let slength := div(and(fslot, sub(mul(0x100, iszero(and(fslot, 1))), 1)), 2)
            let mlength := mload(_postBytes)
            let newlength := add(slength, mlength)
            // slength can contain both the length and contents of the array
            // if length < 32 bytes so let's prepare for that
            // v. http://solidity.readthedocs.io/en/latest/miscellaneous.html#layout-of-state-variables-in-storage
            switch add(lt(slength, 32), lt(newlength, 32))
            case 2 {
                // Since the new array still fits in the slot, we just need to
                // update the contents of the slot.
                // uint256(bytes_storage) = uint256(bytes_storage) + uint256(bytes_memory) + new_length
                sstore(
                    _preBytes_slot,
                    // all the modifications to the slot are inside this
                    // next block
                    add(
                        // we can just add to the slot contents because the
                        // bytes we want to change are the LSBs
                        fslot,
                        add(
                            mul(
                                div(
                                    // load the bytes from memory
                                    mload(add(_postBytes, 0x20)),
                                    // zero all bytes to the right
                                    exp(0x100, sub(32, mlength))
                                ),
                                // and now shift left the number of bytes to
                                // leave space for the length in the slot
                                exp(0x100, sub(32, newlength))
                            ),
                            // increase length by the double of the memory
                            // bytes length
                            mul(mlength, 2)
                        )
                    )
                )
            }
            case 1 {
                // The stored value fits in the slot, but the combined value
                // will exceed it.
                // get the keccak hash to get the contents of the array
                mstore(0x0, _preBytes_slot)
                let sc := add(keccak256(0x0, 0x20), div(slength, 32))

                // save new length
                sstore(_preBytes_slot, add(mul(newlength, 2), 1))

                // The contents of the _postBytes array start 32 bytes into
                // the structure. Our first read should obtain the `submod`
                // bytes that can fit into the unused space in the last word
                // of the stored array. To get this, we read 32 bytes starting
                // from `submod`, so the data we read overlaps with the array
                // contents by `submod` bytes. Masking the lowest-order
                // `submod` bytes allows us to add that value directly to the
                // stored value.

                let submod := sub(32, slength)
                let mc := add(_postBytes, submod)
                let end := add(_postBytes, mlength)
                let mask := sub(exp(0x100, submod), 1)

                sstore(
                    sc,
                    add(
                        and(
                            fslot,
                            0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff00
                        ),
                        and(mload(mc), mask)
                    )
                )

                for {
                    mc := add(mc, 0x20)
                    sc := add(sc, 1)
                } lt(mc, end) {
                    sc := add(sc, 1)
                    mc := add(mc, 0x20)
                } {
                    sstore(sc, mload(mc))
                }

                mask := exp(0x100, sub(mc, end))

                sstore(sc, mul(div(mload(mc), mask), mask))
            }
            default {
                // get the keccak hash to get the contents of the array
                mstore(0x0, _preBytes_slot)
                // Start copying to the last used word of the stored array.
                let sc := add(keccak256(0x0, 0x20), div(slength, 32))

                // save new length
                sstore(_preBytes_slot, add(mul(newlength, 2), 1))

                // Copy over the first `submod` bytes of the new data as in
                // case 1 above.
                let slengthmod := mod(slength, 32)
                let mlengthmod := mod(mlength, 32)
                let submod := sub(32, slengthmod)
                let mc := add(_postBytes, submod)
                let end := add(_postBytes, mlength)
                let mask := sub(exp(0x100, submod), 1)

                sstore(sc, add(sload(sc), and(mload(mc), mask)))

                for {
                    sc := add(sc, 1)
                    mc := add(mc, 0x20)
                } lt(mc, end) {
                    sc := add(sc, 1)
                    mc := add(mc, 0x20)
                } {
                    sstore(sc, mload(mc))
                }

                mask := exp(0x100, sub(mc, end))

                sstore(sc, mul(div(mload(mc), mask), mask))
            }
        }
    }

    function slice(
        bytes memory _bytes,
        uint256 _start,
        uint256 _length
    )
        internal
        pure
        returns (bytes memory)
    {
        require(_length + 31 >= _length, "slice_overflow");
        require(_start + _length >= _start, "slice_overflow");
        require(_bytes.length >= _start + _length, "slice_outOfBounds");

        bytes memory tempBytes;

        assembly {
            switch iszero(_length)
            case 0 {
                // Get a location of some free memory and store it in tempBytes as
                // Solidity does for memory variables.
                tempBytes := mload(0x40)

                // The first word of the slice result is potentially a partial
                // word read from the original array. To read it, we calculate
                // the length of that partial word and start copying that many
                // bytes into the array. The first word we copy will start with
                // data we don't care about, but the last `lengthmod` bytes will
                // land at the beginning of the contents of the new array. When
                // we're done copying, we overwrite the full first word with
                // the actual length of the slice.
                let lengthmod := and(_length, 31)

                // The multiplication in the next line is necessary
                // because when slicing multiples of 32 bytes (lengthmod == 0)
                // the following copy loop was copying the origin's length
                // and then ending prematurely not copying everything it should.
                let mc := add(add(tempBytes, lengthmod), mul(0x20, iszero(lengthmod)))
                let end := add(mc, _length)

                for {
                    // The multiplication in the next line has the same exact purpose
                    // as the one above.
                    let cc := add(add(add(_bytes, lengthmod), mul(0x20, iszero(lengthmod))), _start)
                } lt(mc, end) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    mstore(mc, mload(cc))
                }

                mstore(tempBytes, _length)

                //update free-memory pointer
                //allocating the array padded to 32 bytes like the compiler does now
                mstore(0x40, and(add(mc, 31), not(31)))
            }
            //if we want a zero-length slice let's just return a zero-length array
            default {
                tempBytes := mload(0x40)

                mstore(0x40, add(tempBytes, 0x20))
            }
        }

        return tempBytes;
    }

    function toAddress(bytes memory _bytes, uint256 _start) internal pure returns (address) {
        require(_start + 20 >= _start, "toAddress_overflow");
        require(_bytes.length >= _start + 20, "toAddress_outOfBounds");
        address tempAddress;

        assembly {
            tempAddress := div(mload(add(add(_bytes, 0x20), _start)), 0x1000000000000000000000000)
        }

        return tempAddress;
    }

    function toUint8(bytes memory _bytes, uint256 _start) internal pure returns (uint8) {
        require(_start + 1 >= _start, "toUint8_overflow");
        require(_bytes.length >= _start + 1 , "toUint8_outOfBounds");
        uint8 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x1), _start))
        }

        return tempUint;
    }

    function toUint16(bytes memory _bytes, uint256 _start) internal pure returns (uint16) {
        require(_start + 2 >= _start, "toUint16_overflow");
        require(_bytes.length >= _start + 2, "toUint16_outOfBounds");
        uint16 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x2), _start))
        }

        return tempUint;
    }

    function toUint32(bytes memory _bytes, uint256 _start) internal pure returns (uint32) {
        require(_start + 4 >= _start, "toUint32_overflow");
        require(_bytes.length >= _start + 4, "toUint32_outOfBounds");
        uint32 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x4), _start))
        }

        return tempUint;
    }

    function toUint64(bytes memory _bytes, uint256 _start) internal pure returns (uint64) {
        require(_start + 8 >= _start, "toUint64_overflow");
        require(_bytes.length >= _start + 8, "toUint64_outOfBounds");
        uint64 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x8), _start))
        }

        return tempUint;
    }

    function toUint96(bytes memory _bytes, uint256 _start) internal pure returns (uint96) {
        require(_start + 12 >= _start, "toUint96_overflow");
        require(_bytes.length >= _start + 12, "toUint96_outOfBounds");
        uint96 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0xc), _start))
        }

        return tempUint;
    }

    function toUint128(bytes memory _bytes, uint256 _start) internal pure returns (uint128) {
        require(_start + 16 >= _start, "toUint128_overflow");
        require(_bytes.length >= _start + 16, "toUint128_outOfBounds");
        uint128 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x10), _start))
        }

        return tempUint;
    }

    function toUint256(bytes memory _bytes, uint256 _start) internal pure returns (uint256) {
        require(_start + 32 >= _start, "toUint256_overflow");
        require(_bytes.length >= _start + 32, "toUint256_outOfBounds");
        uint256 tempUint;

        assembly {
            tempUint := mload(add(add(_bytes, 0x20), _start))
        }

        return tempUint;
    }

    function toBytes32(bytes memory _bytes, uint256 _start) internal pure returns (bytes32) {
        require(_start + 32 >= _start, "toBytes32_overflow");
        require(_bytes.length >= _start + 32, "toBytes32_outOfBounds");
        bytes32 tempBytes32;

        assembly {
            tempBytes32 := mload(add(add(_bytes, 0x20), _start))
        }

        return tempBytes32;
    }

    function equal(bytes memory _preBytes, bytes memory _postBytes) internal pure returns (bool) {
        bool success = true;

        assembly {
            let length := mload(_preBytes)

            // if lengths don't match the arrays are not equal
            switch eq(length, mload(_postBytes))
            case 1 {
                // cb is a circuit breaker in the for loop since there's
                //  no said feature for inline assembly loops
                // cb = 1 - don't breaker
                // cb = 0 - break
                let cb := 1

                let mc := add(_preBytes, 0x20)
                let end := add(mc, length)

                for {
                    let cc := add(_postBytes, 0x20)
                // the next line is the loop condition:
                // while(uint256(mc < end) + cb == 2)
                } eq(add(lt(mc, end), cb), 2) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    // if any of these checks fails then arrays are not equal
                    if iszero(eq(mload(mc), mload(cc))) {
                        // unsuccess:
                        success := 0
                        cb := 0
                    }
                }
            }
            default {
                // unsuccess:
                success := 0
            }
        }

        return success;
    }

    function equalStorage(
        bytes storage _preBytes,
        bytes memory _postBytes
    )
        internal
        view
        returns (bool)
    {
        bool success = true;

        assembly {
            // we know _preBytes_offset is 0
            let fslot := sload(_preBytes_slot)
            // Decode the length of the stored array like in concatStorage().
            let slength := div(and(fslot, sub(mul(0x100, iszero(and(fslot, 1))), 1)), 2)
            let mlength := mload(_postBytes)

            // if lengths don't match the arrays are not equal
            switch eq(slength, mlength)
            case 1 {
                // slength can contain both the length and contents of the array
                // if length < 32 bytes so let's prepare for that
                // v. http://solidity.readthedocs.io/en/latest/miscellaneous.html#layout-of-state-variables-in-storage
                if iszero(iszero(slength)) {
                    switch lt(slength, 32)
                    case 1 {
                        // blank the last byte which is the length
                        fslot := mul(div(fslot, 0x100), 0x100)

                        if iszero(eq(fslot, mload(add(_postBytes, 0x20)))) {
                            // unsuccess:
                            success := 0
                        }
                    }
                    default {
                        // cb is a circuit breaker in the for loop since there's
                        //  no said feature for inline assembly loops
                        // cb = 1 - don't breaker
                        // cb = 0 - break
                        let cb := 1

                        // get the keccak hash to get the contents of the array
                        mstore(0x0, _preBytes_slot)
                        let sc := keccak256(0x0, 0x20)

                        let mc := add(_postBytes, 0x20)
                        let end := add(mc, mlength)

                        // the next line is the loop condition:
                        // while(uint256(mc < end) + cb == 2)
                        for {} eq(add(lt(mc, end), cb), 2) {
                            sc := add(sc, 1)
                            mc := add(mc, 0x20)
                        } {
                            if iszero(eq(sload(sc), mload(mc))) {
                                // unsuccess:
                                success := 0
                                cb := 0
                            }
                        }
                    }
                }
            }
            default {
                // unsuccess:
                success := 0
            }
        }

        return success;
    }
}

pragma solidity ^0.5.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

pragma solidity ^0.5.2;
import "./Token.sol";
import "./Math.sol";
import "./Proxy.sol";

/**
 * Deprecated: Use Open Zeppeling one instead
 */
contract StandardTokenData {
    /*
     *  Storage
     */
    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowances;
    uint totalTokens;
}

/**
 * Deprecated: Use Open Zeppeling one instead
 */
/// @title Standard token contract with overflow protection
contract GnosisStandardToken is Token, StandardTokenData {
    using GnosisMath for *;

    /*
     *  Public functions
     */
    /// @dev Transfers sender's tokens to a given address. Returns success
    /// @param to Address of token receiver
    /// @param value Number of tokens to transfer
    /// @return Was transfer successful?
    function transfer(address to, uint value) public returns (bool) {
        if (!balances[msg.sender].safeToSub(value) || !balances[to].safeToAdd(value)) {
            return false;
        }

        balances[msg.sender] -= value;
        balances[to] += value;
        emit Transfer(msg.sender, to, value);
        return true;
    }

    /// @dev Allows allowed third party to transfer tokens from one address to another. Returns success
    /// @param from Address from where tokens are withdrawn
    /// @param to Address to where tokens are sent
    /// @param value Number of tokens to transfer
    /// @return Was transfer successful?
    function transferFrom(address from, address to, uint value) public returns (bool) {
        if (!balances[from].safeToSub(value) || !allowances[from][msg.sender].safeToSub(
            value
        ) || !balances[to].safeToAdd(value)) {
            return false;
        }
        balances[from] -= value;
        allowances[from][msg.sender] -= value;
        balances[to] += value;
        emit Transfer(from, to, value);
        return true;
    }

    /// @dev Sets approved amount of tokens for spender. Returns success
    /// @param spender Address of allowed account
    /// @param value Number of approved tokens
    /// @return Was approval successful?
    function approve(address spender, uint value) public returns (bool) {
        allowances[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    /// @dev Returns number of allowed tokens for given address
    /// @param owner Address of token owner
    /// @param spender Address of token spender
    /// @return Remaining allowance for spender
    function allowance(address owner, address spender) public view returns (uint) {
        return allowances[owner][spender];
    }

    /// @dev Returns number of tokens owned by given address
    /// @param owner Address of token owner
    /// @return Balance of owner
    function balanceOf(address owner) public view returns (uint) {
        return balances[owner];
    }

    /// @dev Returns total supply of tokens
    /// @return Total supply
    function totalSupply() public view returns (uint) {
        return totalTokens;
    }
}

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

pragma solidity ^0.5.0;


library IdToAddressBiMap {
    struct Data {
        mapping(uint16 => address) idToAddress;
        mapping(address => uint16) addressToId;
    }

    function hasId(Data storage self, uint16 id) public view returns (bool) {
        return self.idToAddress[id + 1] != address(0);
    }

    function hasAddress(Data storage self, address addr) public view returns (bool) {
        return self.addressToId[addr] != 0;
    }

    function getAddressAt(Data storage self, uint16 id) public view returns (address) {
        require(hasId(self, id), "Must have ID to get Address");
        return self.idToAddress[id + 1];
    }

    function getId(Data storage self, address addr) public view returns (uint16) {
        require(hasAddress(self, addr), "Must have Address to get ID");
        return self.addressToId[addr] - 1;
    }

    function insert(Data storage self, uint16 id, address addr) public returns (bool) {
        require(addr != address(0), "Cannot insert zero address");
        require(id != uint16(-1), "Cannot insert max uint16");
        // Ensure bijectivity of the mappings
        if (self.addressToId[addr] != 0 || self.idToAddress[id + 1] != address(0)) {
            return false;
        }
        self.idToAddress[id + 1] = addr;
        self.addressToId[addr] = id + 1;
        return true;
    }

}

pragma solidity ^0.5.0;


library IterableAppendOnlySet {
    struct Data {
        mapping(address => address) nextMap;
        address last;
        uint96 size; // width is chosen to align struct size to full words
    }

    function insert(Data storage self, address value) public returns (bool) {
        if (contains(self, value)) {
            return false;
        }
        self.nextMap[self.last] = value;
        self.last = value;
        self.size += 1;
        return true;
    }

    function contains(Data storage self, address value) public view returns (bool) {
        require(value != address(0), "Inserting address(0) is not supported");
        return self.nextMap[value] != address(0) || (self.last == value);
    }

    function first(Data storage self) public view returns (address) {
        require(self.last != address(0), "Trying to get first from empty set");
        return self.nextMap[address(0)];
    }

    function next(Data storage self, address value) public view returns (address) {
        require(contains(self, value), "Trying to get next of non-existent element");
        require(value != self.last, "Trying to get next of last element");
        return self.nextMap[value];
    }
}

pragma solidity ^0.5.2;

/// @title Math library - Allows calculation of logarithmic and exponential functions
/// @author Alan Lu - <alan.lu@gnosis.pm>
/// @author Stefan George - <stefan@gnosis.pm>
library GnosisMath {
    /*
     *  Constants
     */
    // This is equal to 1 in our calculations
    uint public constant ONE = 0x10000000000000000;
    uint public constant LN2 = 0xb17217f7d1cf79ac;
    uint public constant LOG2_E = 0x171547652b82fe177;

    /*
     *  Public functions
     */
    /// @dev Returns natural exponential function value of given x
    /// @param x x
    /// @return e**x
    function exp(int x) public pure returns (uint) {
        // revert if x is > MAX_POWER, where
        // MAX_POWER = int(mp.floor(mp.log(mpf(2**256 - 1) / ONE) * ONE))
        require(x <= 2454971259878909886679);
        // return 0 if exp(x) is tiny, using
        // MIN_POWER = int(mp.floor(mp.log(mpf(1) / ONE) * ONE))
        if (x < -818323753292969962227) return 0;
        // Transform so that e^x -> 2^x
        x = x * int(ONE) / int(LN2);
        // 2^x = 2^whole(x) * 2^frac(x)
        //       ^^^^^^^^^^ is a bit shift
        // so Taylor expand on z = frac(x)
        int shift;
        uint z;
        if (x >= 0) {
            shift = x / int(ONE);
            z = uint(x % int(ONE));
        } else {
            shift = x / int(ONE) - 1;
            z = ONE - uint(-x % int(ONE));
        }
        // 2^x = 1 + (ln 2) x + (ln 2)^2/2! x^2 + ...
        //
        // Can generate the z coefficients using mpmath and the following lines
        // >>> from mpmath import mp
        // >>> mp.dps = 100
        // >>> ONE =  0x10000000000000000
        // >>> print('\n'.join(hex(int(mp.log(2)**i / mp.factorial(i) * ONE)) for i in range(1, 7)))
        // 0xb17217f7d1cf79ab
        // 0x3d7f7bff058b1d50
        // 0xe35846b82505fc5
        // 0x276556df749cee5
        // 0x5761ff9e299cc4
        // 0xa184897c363c3
        uint zpow = z;
        uint result = ONE;
        result += 0xb17217f7d1cf79ab * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x3d7f7bff058b1d50 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0xe35846b82505fc5 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x276556df749cee5 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x5761ff9e299cc4 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0xa184897c363c3 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0xffe5fe2c4586 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x162c0223a5c8 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x1b5253d395e * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x1e4cf5158b * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x1e8cac735 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x1c3bd650 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x1816193 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x131496 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0xe1b7 * zpow / ONE;
        zpow = zpow * z / ONE;
        result += 0x9c7 * zpow / ONE;
        if (shift >= 0) {
            if (result >> (256 - shift) > 0) return (2 ** 256 - 1);
            return result << shift;
        } else return result >> (-shift);
    }

    /// @dev Returns natural logarithm value of given x
    /// @param x x
    /// @return ln(x)
    function ln(uint x) public pure returns (int) {
        require(x > 0);
        // binary search for floor(log2(x))
        int ilog2 = floorLog2(x);
        int z;
        if (ilog2 < 0) z = int(x << uint(-ilog2));
        else z = int(x >> uint(ilog2));
        // z = x * 2^-⌊log₂x⌋
        // so 1 <= z < 2
        // and ln z = ln x - ⌊log₂x⌋/log₂e
        // so just compute ln z using artanh series
        // and calculate ln x from that
        int term = (z - int(ONE)) * int(ONE) / (z + int(ONE));
        int halflnz = term;
        int termpow = term * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 3;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 5;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 7;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 9;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 11;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 13;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 15;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 17;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 19;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 21;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 23;
        termpow = termpow * term / int(ONE) * term / int(ONE);
        halflnz += termpow / 25;
        return (ilog2 * int(ONE)) * int(ONE) / int(LOG2_E) + 2 * halflnz;
    }

    /// @dev Returns base 2 logarithm value of given x
    /// @param x x
    /// @return logarithmic value
    function floorLog2(uint x) public pure returns (int lo) {
        lo = -64;
        int hi = 193;
        // I use a shift here instead of / 2 because it floors instead of rounding towards 0
        int mid = (hi + lo) >> 1;
        while ((lo + 1) < hi) {
            if (mid < 0 && x << uint(-mid) < ONE || mid >= 0 && x >> uint(mid) < ONE) hi = mid;
            else lo = mid;
            mid = (hi + lo) >> 1;
        }
    }

    /// @dev Returns maximum of an array
    /// @param nums Numbers to look through
    /// @return Maximum number
    function max(int[] memory nums) public pure returns (int maxNum) {
        require(nums.length > 0);
        maxNum = -2 ** 255;
        for (uint i = 0; i < nums.length; i++) if (nums[i] > maxNum) maxNum = nums[i];
    }

    /// @dev Returns whether an add operation causes an overflow
    /// @param a First addend
    /// @param b Second addend
    /// @return Did no overflow occur?
    function safeToAdd(uint a, uint b) internal pure returns (bool) {
        return a + b >= a;
    }

    /// @dev Returns whether a subtraction operation causes an underflow
    /// @param a Minuend
    /// @param b Subtrahend
    /// @return Did no underflow occur?
    function safeToSub(uint a, uint b) internal pure returns (bool) {
        return a >= b;
    }

    /// @dev Returns whether a multiply operation causes an overflow
    /// @param a First factor
    /// @param b Second factor
    /// @return Did no overflow occur?
    function safeToMul(uint a, uint b) internal pure returns (bool) {
        return b == 0 || a * b / b == a;
    }

    /// @dev Returns sum if no overflow occurred
    /// @param a First addend
    /// @param b Second addend
    /// @return Sum
    function add(uint a, uint b) internal pure returns (uint) {
        require(safeToAdd(a, b));
        return a + b;
    }

    /// @dev Returns difference if no overflow occurred
    /// @param a Minuend
    /// @param b Subtrahend
    /// @return Difference
    function sub(uint a, uint b) internal pure returns (uint) {
        require(safeToSub(a, b));
        return a - b;
    }

    /// @dev Returns product if no overflow occurred
    /// @param a First factor
    /// @param b Second factor
    /// @return Product
    function mul(uint a, uint b) internal pure returns (uint) {
        require(safeToMul(a, b));
        return a * b;
    }

    /// @dev Returns whether an add operation causes an overflow
    /// @param a First addend
    /// @param b Second addend
    /// @return Did no overflow occur?
    function safeToAdd(int a, int b) internal pure returns (bool) {
        return (b >= 0 && a + b >= a) || (b < 0 && a + b < a);
    }

    /// @dev Returns whether a subtraction operation causes an underflow
    /// @param a Minuend
    /// @param b Subtrahend
    /// @return Did no underflow occur?
    function safeToSub(int a, int b) internal pure returns (bool) {
        return (b >= 0 && a - b <= a) || (b < 0 && a - b > a);
    }

    /// @dev Returns whether a multiply operation causes an overflow
    /// @param a First factor
    /// @param b Second factor
    /// @return Did no overflow occur?
    function safeToMul(int a, int b) internal pure returns (bool) {
        return (b == 0) || (a * b / b == a);
    }

    /// @dev Returns sum if no overflow occurred
    /// @param a First addend
    /// @param b Second addend
    /// @return Sum
    function add(int a, int b) internal pure returns (int) {
        require(safeToAdd(a, b));
        return a + b;
    }

    /// @dev Returns difference if no overflow occurred
    /// @param a Minuend
    /// @param b Subtrahend
    /// @return Difference
    function sub(int a, int b) internal pure returns (int) {
        require(safeToSub(a, b));
        return a - b;
    }

    /// @dev Returns product if no overflow occurred
    /// @param a First factor
    /// @param b Second factor
    /// @return Product
    function mul(int a, int b) internal pure returns (int) {
        require(safeToMul(a, b));
        return a * b;
    }
}

pragma solidity ^0.5.0;

import "../GSN/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

pragma solidity ^0.5.2;

/// @title Proxied - indicates that a contract will be proxied. Also defines storage requirements for Proxy.
/// @author Alan Lu - <alan@gnosis.pm>
contract Proxied {
    address public masterCopy;
}

/// @title Proxy - Generic proxy contract allows to execute all transactions applying the code of a master contract.
/// @author Stefan George - <stefan@gnosis.pm>
contract Proxy is Proxied {
    /// @dev Constructor function sets address of master copy contract.
    /// @param _masterCopy Master copy address.
    constructor(address _masterCopy) public {
        require(_masterCopy != address(0), "The master copy is required");
        masterCopy = _masterCopy;
    }

    /// @dev Fallback function forwards all transactions and returns all received return data.
    function() external payable {
        address _masterCopy = masterCopy;
        assembly {
            calldatacopy(0, 0, calldatasize)
            let success := delegatecall(not(0), _masterCopy, 0, calldatasize, 0, 0)
            returndatacopy(0, 0, returndatasize)
            switch success
                case 0 {
                    revert(0, returndatasize)
                }
                default {
                    return(0, returndatasize)
                }
        }
    }
}

pragma solidity ^0.5.0;


/**
 * @dev Wrappers over Solidity's uintXX casting operators with added overflow
 * checks.
 *
 * Downcasting from uint256 in Solidity does not revert on overflow. This can
 * easily result in undesired exploitation or bugs, since developers usually
 * assume that overflows raise errors. `SafeCast` restores this intuition by
 * reverting the transaction when such an operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 *
 * Can be combined with {SafeMath} to extend it to smaller types, by performing
 * all math on `uint256` and then downcasting.
 *
 * _Available since v2.5.0._
 */
library SafeCast {

    /**
     * @dev Returns the downcasted uint128 from uint256, reverting on
     * overflow (when the input is greater than largest uint128).
     *
     * Counterpart to Solidity's `uint128` operator.
     *
     * Requirements:
     *
     * - input must fit into 128 bits
     */
    function toUint128(uint256 value) internal pure returns (uint128) {
        require(value < 2**128, "SafeCast: value doesn\'t fit in 128 bits");
        return uint128(value);
    }

    /**
     * @dev Returns the downcasted uint64 from uint256, reverting on
     * overflow (when the input is greater than largest uint64).
     *
     * Counterpart to Solidity's `uint64` operator.
     *
     * Requirements:
     *
     * - input must fit into 64 bits
     */
    function toUint64(uint256 value) internal pure returns (uint64) {
        require(value < 2**64, "SafeCast: value doesn\'t fit in 64 bits");
        return uint64(value);
    }

    /**
     * @dev Returns the downcasted uint32 from uint256, reverting on
     * overflow (when the input is greater than largest uint32).
     *
     * Counterpart to Solidity's `uint32` operator.
     *
     * Requirements:
     *
     * - input must fit into 32 bits
     */
    function toUint32(uint256 value) internal pure returns (uint32) {
        require(value < 2**32, "SafeCast: value doesn\'t fit in 32 bits");
        return uint32(value);
    }

    /**
     * @dev Returns the downcasted uint16 from uint256, reverting on
     * overflow (when the input is greater than largest uint16).
     *
     * Counterpart to Solidity's `uint16` operator.
     *
     * Requirements:
     *
     * - input must fit into 16 bits
     */
    function toUint16(uint256 value) internal pure returns (uint16) {
        require(value < 2**16, "SafeCast: value doesn\'t fit in 16 bits");
        return uint16(value);
    }

    /**
     * @dev Returns the downcasted uint8 from uint256, reverting on
     * overflow (when the input is greater than largest uint8).
     *
     * Counterpart to Solidity's `uint8` operator.
     *
     * Requirements:
     *
     * - input must fit into 8 bits.
     */
    function toUint8(uint256 value) internal pure returns (uint8) {
        require(value < 2**8, "SafeCast: value doesn\'t fit in 8 bits");
        return uint8(value);
    }
}

pragma solidity ^0.5.0;

import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

pragma solidity ^0.5.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

pragma solidity ^0.5.0;

/**
 * @title SignedSafeMath
 * @dev Signed math operations with safety checks that revert on error.
 */
library SignedSafeMath {
    int256 constant private INT256_MIN = -2**255;

    /**
     * @dev Multiplies two signed integers, reverts on overflow.
     */
    function mul(int256 a, int256 b) internal pure returns (int256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        require(!(a == -1 && b == INT256_MIN), "SignedSafeMath: multiplication overflow");

        int256 c = a * b;
        require(c / a == b, "SignedSafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
     */
    function div(int256 a, int256 b) internal pure returns (int256) {
        require(b != 0, "SignedSafeMath: division by zero");
        require(!(b == -1 && a == INT256_MIN), "SignedSafeMath: division overflow");

        int256 c = a / b;

        return c;
    }

    /**
     * @dev Subtracts two signed integers, reverts on overflow.
     */
    function sub(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a), "SignedSafeMath: subtraction overflow");

        return c;
    }

    /**
     * @dev Adds two signed integers, reverts on overflow.
     */
    function add(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a), "SignedSafeMath: addition overflow");

        return c;
    }
}

/// Implements ERC 20 Token standard: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
pragma solidity ^0.5.2;

/// @title Abstract token contract - Functions to be implemented by token contracts
contract Token {
    /*
     *  Events
     */
    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);

    /*
     *  Public functions
     */
    function transfer(address to, uint value) public returns (bool);
    function transferFrom(address from, address to, uint value) public returns (bool);
    function approve(address spender, uint value) public returns (bool);
    function balanceOf(address owner) public view returns (uint);
    function allowance(address owner, address spender) public view returns (uint);
    function totalSupply() public view returns (uint);
}

pragma solidity ^0.5.2;

import "@gnosis.pm/util-contracts/contracts/Math.sol";
import "@gnosis.pm/util-contracts/contracts/GnosisStandardToken.sol";
import "@gnosis.pm/util-contracts/contracts/Proxy.sol";

contract TokenOWL is Proxied, GnosisStandardToken {
    using GnosisMath for *;

    string public constant name = "OWL Token";
    string public constant symbol = "OWL";
    uint8 public constant decimals = 18;

    struct masterCopyCountdownType {
        address masterCopy;
        uint timeWhenAvailable;
    }

    masterCopyCountdownType masterCopyCountdown;

    address public creator;
    address public minter;

    event Minted(address indexed to, uint256 amount);
    event Burnt(address indexed from, address indexed user, uint256 amount);

    modifier onlyCreator() {
        // R1
        require(msg.sender == creator, "Only the creator can perform the transaction");
        _;
    }
    /// @dev trickers the update process via the proxyMaster for a new address _masterCopy
    /// updating is only possible after 30 days
    function startMasterCopyCountdown(address _masterCopy) public onlyCreator {
        require(address(_masterCopy) != address(0), "The master copy must be a valid address");

        // Update masterCopyCountdown
        masterCopyCountdown.masterCopy = _masterCopy;
        masterCopyCountdown.timeWhenAvailable = now + 30 days;
    }

    /// @dev executes the update process via the proxyMaster for a new address _masterCopy
    function updateMasterCopy() public onlyCreator {
        require(address(masterCopyCountdown.masterCopy) != address(0), "The master copy must be a valid address");
        require(
            block.timestamp >= masterCopyCountdown.timeWhenAvailable,
            "It's not possible to update the master copy during the waiting period"
        );

        // Update masterCopy
        masterCopy = masterCopyCountdown.masterCopy;
    }

    function getMasterCopy() public view returns (address) {
        return masterCopy;
    }

    /// @dev Set minter. Only the creator of this contract can call this.
    /// @param newMinter The new address authorized to mint this token
    function setMinter(address newMinter) public onlyCreator {
        minter = newMinter;
    }

    /// @dev change owner/creator of the contract. Only the creator/owner of this contract can call this.
    /// @param newOwner The new address, which should become the owner
    function setNewOwner(address newOwner) public onlyCreator {
        creator = newOwner;
    }

    /// @dev Mints OWL.
    /// @param to Address to which the minted token will be given
    /// @param amount Amount of OWL to be minted
    function mintOWL(address to, uint amount) public {
        require(minter != address(0), "The minter must be initialized");
        require(msg.sender == minter, "Only the minter can mint OWL");
        balances[to] = balances[to].add(amount);
        totalTokens = totalTokens.add(amount);
        emit Minted(to, amount);
        emit Transfer(address(0), to, amount);
    }

    /// @dev Burns OWL.
    /// @param user Address of OWL owner
    /// @param amount Amount of OWL to be burnt
    function burnOWL(address user, uint amount) public {
        allowances[user][msg.sender] = allowances[user][msg.sender].sub(amount);
        balances[user] = balances[user].sub(amount);
        totalTokens = totalTokens.sub(amount);
        emit Burnt(msg.sender, user, amount);
        emit Transfer(user, address(0), amount);
    }

    function getMasterCopyCountdown() public view returns (address, uint) {
        return (masterCopyCountdown.masterCopy, masterCopyCountdown.timeWhenAvailable);
    }
}

{
  "compilationTarget": {
    "/Users/felixleupold/Gnosis/dex-contracts/contracts/SolutionSubmitter.sol": "SolutionSubmitter"
  },
  "evmVersion": "petersburg",
  "libraries": {},
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}