Add 2.5 and 2.6

2_5.sch

@@ -0,0 +1,18 @@
+(define (cons a b)
+  (* (power 2 a) (power 3 b)))
+
+(define (power x n)
+  (if (= n 0)
+      1
+      (* x (power x (- n 1)))))
+
+(define (iter x n p)
+  (if (> (remainder x n) 0)
+      p
+      (iter (quotient x n) n (+ 1 p))))
+
+(define (car z)
+  (iter z 2 0))
+
+(define (cdr z)
+  (iter z 3 0))

2_6.sch

@@ -0,0 +1,13 @@
+(define zero (lambda (f) (lambda (x) x)))
+
+(define (add-1 n)
+  (lambda (f) (lambda (x) (f ((n f) x)))))
+
+(define one
+  (lambda (f) (lambda (x) (f x))))
+
+(define two
+  (lambda (f) (lambda (x) (f (f x)))))
+
+(define (plus a b)
+  (lambda (f) (lambda (x) ((a f) ((b f) x)))))