SICP Practice

Practice 3.39

	(* 10 10)
	(set! x 100)
	(set! x (+ 100 1))
	; 101

	(set! x (+ 10 1))
	(* 11 11)
	(set! x 121)
	; 121

	(* 10 10)
	(set! x (+ 10 1))
	(set! x 100)
	; 100