2.54.scm

(define (equal? l1 l2)
  (cond  ((and (null? l1) (null? l2)) #t)
         ((and (symbol? l1) (symbol? l2)) (eq? l1 l2))
         ((and (pair? l1) (pair? l2)
               (equal? (car l1) (car l2)) (equal? (cdr l1) (cdr l2))) #t)
         (else #f)))