function underlyingBalance() public view returns (uint256) {
    uint256 _pool = IERC20(underlyingToken).balanceOf(address(this));
    return _pool.add(outstandingAmount);
}
function removeFilledTradeAmount(uint256 amt) external onlyPair {
    outstandingAmount = outstandingAmount.sub(amt);
    emit LogRemoveFilledTradeAmount(
        IERC20(underlyingToken),
        amt,
        underlyingBalance(),
        outstandingAmount,
        totalSupply
    );
}
