LOGIKA

(define (var? e)
  (boolean? e))

(define (disj? e)
  (and (list? e)
       (= (length e) 3)
       (eq? (car e) 'disj)))

(define (conj? e)
  (and (list? e)
       (= (length e) 3)
       (eq? (car e) 'conj)))

(define (op-left e)
  (second e))

(define (op-right e)
  (third e))

(define (leval e)
  (cond [(var? e) e]
        [(disj? e)
         (or
          (leval (op-left e))
          (leval (op-right e)))]
        [(conj? e)
         (and
          (leval (op-left e))
          (leval (op-right e)))]))