A company stores all the purchase orders placed by it on its vendors in a purchase order file (POFILE). When it receives delivery of goods against a purchase order the details are entered
in a file called RECDPOFILE (assume that partial deliveries do not exist, and that a purchase order corresponds to only one product). When an invoice is received from a vendor t is
stored in the INVCEFILE. At the end of each day, a program retrieves each invoice in the
INVCEFILE, checks it for the following: