Apply the WHERE clause.
BUTTON1:
   listid=makelist();
   listid=insertc(listid, 'Sex="M"', -1);
   listid=insertc(listid, 'and weight > 50',
                  -1);
   call putlist(listid, 'WHERE clause=', 0);
   call send(datid, '_setWhere', listid);
   rc=clearlist(listid);