comparing data in two spreadsheet
 

I have 2 spreadsheet. I have in column A invoice number in both spreadsheet.
In In speadsheet one (AR 2005 outstanding invoices.xls ) the invoice is only
listed once. However, in the 2nd spreadsheet , (2005sales.csv) t may be
listed more than once. I want spreadsheet 2005sales.csv to compare column A
(Invoice/CM# with column A (Invoice/CM#) in AR 2005 outstanding Invoices.xls
and return the value true or false so that I can sort 2005sales.csv and
delete the Invoice numbers that don't match.