;;z evala
[(num? e)
         (let ([possible-nr (num?-num e)])
           (if (var? possible-nr)
               (if (number? (find-in-env possible-nr env))
                   'true
                   'false
                   )
               (if (number? possible-nr)
                   'true
                   'false
                   )
               )
           )
         ]
;;


(define (num? x)
  (tagged-tuple? 'number? 2 x))

(define (num?-cons num)
  (list number? num))

(define (num?-num num)
  (cadr num))

(eval '((lambda-rec (eval expr)
                  (cond [(number? expr)
                         expr]
                        ;[(operator? )]
                        )
                  ) 2)
      )