func: function multitokenChangeAmount(IMultiToken mtkn, ERC20 fromToken, ERC20 toToken, uint256 minReturn, uint256 amount) external {
          if (fromToken.allowance(this, mtkn) == 0) {
              fromToken.asmApprove(mtkn, uint256(-1));
          }
          mtkn.change(fromToken, toToken, amount, minReturn);
      }