gistfile1.txt

thing
= (list 1 2 3 4) 
= (1 . (2 . (3 . (4 . nil))))

(car thing)
= 1

(cdr thing)
= (2 . (3 . (4 . nil)))
= cdr_thing

(cdr (cdr thing))
= (3 . (4 . nil))
= cdrcdr_thing

(cdr (cdr (cdr thing)))
= (4 . nil)
= cdrcdrcdr_thing

(define (car x) carmap[x])
(define (cdr x) cdrmap[x])

carmap = {
    thing: 1
    cdr_thing: 2
    cdrcdr_thing: 3
    cdrcdrcdr_thing: 4
}

cdrmap = {
    thing: cdr_thing
    cdr_thing: cdrcdr_thing
    cdrcdr_thing: cdrcdrcdr_thing
    cdrcdrcdr_thing: nil
}