4 (not (eq? (car x) 'let))
5 (not (eq? (car x) 'lambda))))
8 (and (list? x) (eq? (car x) 'let)))
10 (define let-bindings cadr)
11 (define let-body cddr)
14 (and (list? x) (eq? (car x) 'lambda)))
16 (define lambda-arg cadr)
17 (define lambda-body cddr)
20 (and (not (list? x)) (symbol? x)))