Duplicate invoice. Query help needed

Hi All,

We need to build a query which addresses the following condition
Some of the invoices were created against the wrong vendors and that money needs to be recovered. Some of them are already recovered while some are not
* list out all the duplicate invoices between a particular date range(invoice date) with same invoice num ,same invoice amount and same invoice date.
* If there are any debit invoice created(invoice number postfixed with CR or ADJ),those particualr invoices should not be included.
The table below shows two type of invoice, the one with red color(invoice num=193666) has debit invocie created and all the three records related to it should not be a part of output data
while the record(invoice num=00017321) should be a part of output data.

INVOICE_NUM INVOICE_AMOUNT VENDOR_NUMBER INVOICE_DATE ORG_ID
00017321 233.35 A321 1-Dec-11 95
00017321 233.35 K452 1-Dec-11 95
193666 101.67 EM9B 18-May-12 91
193666 101.67 1B02 18-May-12 91
193666CR -101.67 1B02 18-May-12 91


Below is the query which i wrote to identify the duplicate invoice


select distinct
a1.invoice_amount,
a1.invoice_num,
(select segment1 from apps.po_vendors where vendor_id=a1.vendor_id) vendor_name,
a1.invoice_date,
A1.ORG_ID
from apps.ap_invoices_all a1,
apps.ap_invoices_all a2
where 1=1
and a1.org_id in (91,95)
and a1.org_id in (91,95)
and a1.invoice_date between (to_DATE('01-SEP-2011','DD-MON-YYYY')) AND (to_DATE('01-JUN-2012','DD-MON-YYYY'))
and a2.invoice_date between (to_DATE('01-SEP-2011','DD-MON-YYYY')) AND (to_DATE('01-JUN-2012','DD-MON-YYYY'))
and a2.invoice_num=a1.invoice_num
and a1.invoice_amount=a2.invoice_amount
and a1.invoice_id<>a2.invoice_id
and a1.invoice_amount<>0
order by a1.invoice_amount,a1.invoice_num

Can anybody share their thoughts on how to modify the query above which checks if there are any debit invoice created and not include in the final output.

Thanks in advance