(defun eval. (e a)
  (cond
    ((atom e) (assoc. e a))
    ((atom (car e))
     (cond
       ((eq (car e) 'quote) (cadr e))
       ((eq (car e) 'atom) (atom (eval. (cadr e) a)))
       ((eq (car e) 'eq) (eq (eval. (cadr e) a)
                             (eval. (caddr e) a)))
       ((eq (car e) 'car) (car (eval. (cadr e) a)))
       ((eq (car e) 'cdr) (cdr (eval. (cadr e) a)))
       ((eq (car e) 'cons) (cons (eval. (cadr e) a)
                                 (eval. (caddr e) a)))
       ((eq (car e) 'cond) (evcon. (cdr e) a))
       ('t (eval. (cons (assoc. (car e) a)
                        (cdr e))
                  a))))
    ((eq (caar e) 'label)
     (eval. (cons (caddar e) (cdr e))
            (cons (list (cadar e) (car e)) a)))
    ((eq (caar e) 'lambda)
     (eval. (caddar e)
            (append. (pair. (cadar e) (evlis. (cdr e) a))
                     a)))))

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