function continueOrder(uint128 orderId, uint maxMatches) public {
    address client = msg.sender;
    Order storage order = orderForOrderId[orderId];
    require(order.client == client);
    if (order.status != Status.NeedsGas) {
      return;
    }
    order.status = Status.Unknown;
    processOrder(orderId, maxMatches);
  }