public IEnumerable <LimitOrder> DeleteMarketMakerOrders(string marketMakerId, string[] idsToDelete)
{
var deletedBuy = Buy.DeleteMarketMakerOrders(marketMakerId, idsToDelete);
var deletedSell = Sell.DeleteMarketMakerOrders(marketMakerId, idsToDelete);
return(deletedBuy.Concat(deletedSell));
}