XLISP-PLUS version 3.04
Portions Copyright (c) 1988, by David Betz.
Modified by Thomas Almy and others.
XLISP-STAT Release 3.52.17 (Beta).
Copyright (c) 1989-1999, by Luke Tierney.

> (defun memset (sex lis) (cond
                            ((null lis)       nil)
                            ((equal (first lis) sex)   t)
                            ('else   (memset sex (rest lis)))
))
MEMSET
> (memset 'a '(a b))
T
> (member 'b '(a b))
(B)
>  (memset 'b '(a b))
T
> (memset 'c '(a b))
NIL
> (defun myap (l1 l2) (cond
                        ((null l1)    l2)
                        ((null l2)    l1)
                        ('else (cons (first l1) (myap (rest l1) l2)))
))
MYAP
> (myap '(a) '(a b))
(A A B)
> (myap '(b) '(a b))
(B A B)
> (myap nil '(a b))
(A B)
> (myap '(a b) nil)
(A B)
> (myap '(a b) '(c d))
(A B C D)
> (trace myap)
(MYAP)
> (myap '(a b) '( c d))
Entering: MYAP, Argument list: ((A B) (C D))
 Entering: MYAP, Argument list: ((B) (C D))
  Entering: MYAP, Argument list: (NIL (C D))
  Exiting: MYAP, Value: (C D)
 Exiting: MYAP, Value: (B C D)
Exiting: MYAP, Value: (A B C D)
(A B C D)
>