Hi,
I think the simplest way is break this SQL statement into 2.

select memb_folio ;
FROM demat WHERE qty_accept > 0 ;
AND demat_no NOT in(select trfno FROM wcert) ;
INTO CURSOR myCursor

SELECT DISTINCT sfolio ;
FROM folio ;
WHERE sfolio in(SELECT memb_folio FROM myCursor)

If you are using view, then you may create 2 views, each for SQL above (without INTO CURSOR clause).

HTH