Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0;

import "./interfaces/IERC20.sol";
import "@openzeppelin/contracts/proxy/Proxy.sol";

contract SigmaFallThrough is Proxy {
  address internal constant FFF = 0xaBAfA52D3d5A2c18A4C1Ae24480D22B831fC0413;
  address internal immutable drainReversalImplementation;

  constructor(address _drainReversalImplementation) {
    drainReversalImplementation = _drainReversalImplementation;
  }

  function _implementation() internal view virtual override returns (address) {
    if (address(this) == FFF) {
      return drainReversalImplementation;
    }
    return 0x7B3B2B39CbdBddaDC13D8559D82c054b9C2fd5f3;
  }
}

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0;

interface IERC20 {
  event Approval(address indexed src, address indexed dst, uint256 amt);
  event Transfer(address indexed src, address indexed dst, uint256 amt);

  function symbol() external view returns (string memory);

  function name() external view returns (string memory);

  function decimals() external view returns (uint8);

  function totalSupply() external view returns (uint256);

  function balanceOf(address account) external view returns (uint256);

  function transfer(address recipient, uint256 amount) external returns (bool);

  function allowance(address owner, address spender)
    external
    view
    returns (uint256);

  function approve(address spender, uint256 amount) external returns (bool);

  function transferFrom(
    address sender,
    address recipient,
    uint256 amount
  ) external returns (bool);
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM
 * instruction `delegatecall`. We refer to the second contract as the _implementation_ behind the proxy, and it has to
 * be specified by overriding the virtual {_implementation} function.
 *
 * Additionally, delegation to the implementation can be triggered manually through the {_fallback} function, or to a
 * different contract through the {_delegate} function.
 *
 * The success and return data of the delegated call will be returned back to the caller of the proxy.
 */
abstract contract Proxy {
    /**
     * @dev Delegates the current call to `implementation`.
     *
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _delegate(address implementation) internal virtual {
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // Copy msg.data. We take full control of memory in this inline assembly
            // block because it will not return to Solidity code. We overwrite the
            // Solidity scratch pad at memory position 0.
            calldatacopy(0, 0, calldatasize())

            // Call the implementation.
            // out and outsize are 0 because we don't know the size yet.
            let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)

            // Copy the returned data.
            returndatacopy(0, 0, returndatasize())

            switch result
            // delegatecall returns 0 on error.
            case 0 { revert(0, returndatasize()) }
            default { return(0, returndatasize()) }
        }
    }

    /**
     * @dev This is a virtual function that should be overriden so it returns the address to which the fallback function
     * and {_fallback} should delegate.
     */
    function _implementation() internal view virtual returns (address);

    /**
     * @dev Delegates the current call to the address returned by `_implementation()`.
     *
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _fallback() internal virtual {
        _beforeFallback();
        _delegate(_implementation());
    }

    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if no other
     * function in the contract matches the call data.
     */
    fallback () external payable virtual {
        _fallback();
    }

    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if call data
     * is empty.
     */
    receive () external payable virtual {
        _fallback();
    }

    /**
     * @dev Hook that is called before falling back to the implementation. Can happen as part of a manual `_fallback`
     * call, or as part of the Solidity `fallback` or `receive` functions.
     *
     * If overriden should call `super._beforeFallback()`.
     */
    function _beforeFallback() internal virtual {
    }
}