% (boolean? #t)
#t
% (boolean? 3)
#f
% (define three 3)
nil
% three
3
% (+ three 4)
7
% (define add-two (lambda (n) (+ n 2)))
nil
% (add-two 5)
7
% (define fact (lambda (n) (if (= n 0) 1 (* n (fact (- n 1))))))
nil
% (fact 3)
6
% (fact 5)
120