(DEFINE MEMQ , (LAMBDA (S L) , , (PROG (P) , , , (SETQ P L) , , , (REPEAT , , , , UNTIL (NULL P) , , , , UNTIL (EQ (CAR P) S) , , , , (SETQ P (CDR P)) , , , ,,,) , , , (RETURN (NOT (NULL P))) , , ,,,) , ,,,) ,,,)