From 8ecb5a852d21e82fa1c986c8d142303a3ebbf3de Mon Sep 17 00:00:00 2001
From: Marcin Gryszko <marcin@grysz.com>
Date: Wed, 18 Apr 2012 21:56:10 +0200
Subject: [PATCH] 1.2.4 completed

---
 ex1.16.scm |  1 +
 ex1.17.scm | 18 ++++++++++++++++++
 ex1.18.scm |  0
 ex1.19.scm | 14 ++++++++++++++
 4 files changed, 33 insertions(+)
 create mode 100644 ex1.16.scm
 create mode 100644 ex1.17.scm
 create mode 100644 ex1.18.scm
 create mode 100644 ex1.19.scm

diff --git a/ex1.16.scm b/ex1.16.scm
new file mode 100644
index 0000000..96026ee
--- /dev/null
+++ b/ex1.16.scm
@@ -0,0 +1 @@
+`xzc`xc
\ No newline at end of file
diff --git a/ex1.17.scm b/ex1.17.scm
new file mode 100644
index 0000000..e33483c
--- /dev/null
+++ b/ex1.17.scm
@@ -0,0 +1,18 @@
+(define (even? n)
+  (= (remainder n 2) 0))
+
+(define (halve n)
+  (/ n 2))
+
+(define (double n)
+  (+ n n))
+
+(define (* a b)
+  (cond ((= b 0) 0)
+	((even? b) (* (double a) (halve b)))
+	(else (+ a (* a (- b 1))))))
+      
+(* 2 2)
+(* 3 4)
+(* 15 11)
+
diff --git a/ex1.18.scm b/ex1.18.scm
new file mode 100644
index 0000000..e69de29
diff --git a/ex1.19.scm b/ex1.19.scm
new file mode 100644
index 0000000..9886ee7
--- /dev/null
+++ b/ex1.19.scm
@@ -0,0 +1,14 @@
+(define (fib n)
+  (fib-iter 1 0 0 1 n))
+
+(define (fib-iter a b p q count)
+  (cond ((= count 0) b)
+        ((even? count) (fib-iter a 
+				 b
+				 <??> ; compute p’
+				 <??> ; compute q’ (/ count 2)))
+        (else (fib-iter (+ (* b q) (* a q) (* a p))
+                        (+ (* b p) (* a q))
+                        p
+                        q
+                        (- count 1)))))
\ No newline at end of file