i.e.
select * from purchase_requests pr,parts p
where p.part = pr.part and p.cage = pr.cage
and pr.status = 'O'
and (pr.order_no = 'REF' or pr.purchase_order = 'REF' or p.nsn = 'REF' or p.stock_number = 'REF')
allowing you to add pr.order_no and pr.purchaseh_order within the same AtomicCriteria as p.nsn and p.stock_number