Didn't work,
@in period
//IIF ({OPP0100_HIST_LAST.BKDATE}>={PAY_PERIOD.BEGIN_DT},True , False)
//IIF ({PAYABLES_LEDGER.PAY_DATE}>={PAY_PERIOD.BEGIN_DT},True , False)
IIF ({PAYABLES_LEDGER.PAY_DATE}={PAY_PERIOD.PAY_DATE},True , False)
@in period counter
IIF ({@in period},1 ,0 )
@prior period...