public void sell(ProductTransactionItem pti, DateTime date, string not = null, bool isPaid = true, Contact con = null, Check chk = null)
{
List <ProductTransactionItem> list = new List <ProductTransactionItem>();
list.Add(pti);
sell(list, date, not, isPaid, con, chk);
}
public void buy(ProductTransactionItem pti, DateTime date, string not = null, bool isPaid = true, Contact con = null, Check chk = null)
{
}