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#lang racket
(provide conj conj-left conj-right conj?
disj disj-left disj-right disj?
neg neg-subf neg?
var?)
(define (conj p q)
(list 'conj p q))
(define (conj-left f)
(second f))
(define (conj-right f)
(third f))
(define (conj? t)
(and (list? t)
(= 3 (length t))
(eq? 'conj (car t))))
(define (disj p q)
(list 'disj p q))
(define (disj-left f)
(second f))
(define (disj-right f)
(third f))
(define (disj? t)
(and (list? t)
(= 3 (length t))
(eq? 'disj (car t))))
(define (neg x)
(list 'neg x))
(define (neg-subf x)
(second x))
(define (neg? t)
(and (list? t)
(= 2 (length t))
(eq? 'neg (car t))))
(define (var? t)
(symbol? t))
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