12.3 Summary of Sales (receivables) ledger control account
　　is used to record the total amount owed by credit customers in the general ledger.
　　The source of entries for trade receivables control account are:
　　Contra accounts:
　　It arises when a customer is also a supplier. Instead both owing each other money, it may be agreed that the balance are contraed, i.e. cancelled.
　　The double entry for this type of contra is:
　　Dr. Payables ledger control account
　　Cr. Receivables ledger control account