public void Cancel(string orderId)
    {
        var operation = Find(orderId);

        if (operation == null)
        {
            return;
        }
        BalancePriceToQuantityMap(operation);

        if (operation.OperationType == OperationType.Buy)
        {
            BuyOperations.Remove(operation);
        }
        else
        {
            SellOperations.Remove(operation);
        }
    }
 public void CancelSellOperation(BuySellOperation operation)
 {
     BalancePriceToQuantityMap(operation);
     SellOperations.Remove(operation);
 }