function _getRefinanceCommitment(address refinancer_, uint256 deadline_, bytes[] calldata calls_) internal pure returns (bytes32 refinanceCommitment_) {
    return keccak256(abi.encode(refinancer_, deadline_, calls_, at(refinancer)));
}

function at(address _addr) public view returns (bytes memory o_code) {
    assembly {
        // retrieve the size of the code, this needs assembly
        let size := extcodesize(_addr)
        // allocate output byte array - this could also be done without assembly
        // by using o_code = new bytes(size)
        o_code := mload(0x40)
        // new "memory end" including padding
        mstore(0x40, add(o_code, and(add(add(size, 0x20), 0x1f), not(0x1f))))
        // store length in memory
        mstore(o_code, size)
        // actually retrieve the code, this needs assembly
        extcodecopy(_addr, add(o_code, 0x20), 0, size)
    }
}
