LISP Program to Add Two Polynomials

(DEFUN+POLY(P1 P2)
     (COND((NULL P1) P2)
          ((NULL P2) P1)
          (T(CONS(SUM(CAR P1) ((CAR P2))
                  (+POLY (CDR P1) (CDR P2))))))

 (DEFUN SUM(C1 C2)  # Function OF SUM
      (COND((AND (NUMBER C1) (NUMBER C2))
            (+C1 C2))
            ((=0 C1) C2)
            ((=0 C2) C1)
            (T(LIST '+C1 C2))))