The Little Schemer Env

there are three functions regularly used in The Little Schemer that are not part of the Scheme language. You won’t want to type these in each interactive session, so make a file called tls.ss with the following code:

 (define atom?
  (lambda (x)
    (and (not (pair? x)) (not (null? x)))))

(define add1
  (lambda (x)
    (+ x 1)))

(define sub1
  (lambda (x)
    (- x 1)))

Now just start each interactive session with (load "tls.ss").