func: function removeSellOrder(uint _key) public {
          uint order = orderBook.get(_key);
          ORDER_TYPE orderType = ORDER_TYPE(order >> 254);
          require(orderType == ORDER_TYPE.SELL, "This is not a sell order");
          uint index = addressIndex[msg.sender];
          require(index == (order << 2) >> 224, "You are not the sender of this order");
  
          uint price = (order << 34) >> 145;
          uint amount = (order << 145) >> 145;
          require(orderBook.remove(_key), "Map remove failed");
  
          uint orderFee = feeForOrder(price, amount);
          if (orderFee > 0) {
              feeBalances[index] = feeBalances[index].add(orderFee);
          }
  
          poolOwners.sendOwnership(msg.sender, amount);
  
          emit OrderRemoved(orderType, msg.sender, price, amount);
      }