diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,6 @@
-# Makefile
+# Makefile for RPN
+# (c) 2005 Horst H. von Brand
+# Licensed under the Open Software License version 2.1
 
 rpn: rpn.o stack.o lexer.o
 	$(CC) $(CFLAGS) $^ -o $@
diff --git a/lexer.c b/lexer.c
--- a/lexer.c
+++ b/lexer.c
@@ -1,5 +1,8 @@
 /*
- * lexer.c
+ * lexer.c -- Lexical analysis for RPN
+ *
+ * (c) 2005 Horst H. von Brand
+ * Licensed under the Open Software License version 2.1
  */
 
 #include <stdio.h>
diff --git a/rpn.c b/rpn.c
--- a/rpn.c
+++ b/rpn.c
@@ -1,5 +1,8 @@
 /*
- * rpn.c
+ * rpn.c -- Main program for RPN
+ *
+ * (c) 2005 Horst H. von Brand
+ * Licensed under the Open Software License version 2.1
  */
 
 #include <stdio.h>
diff --git a/stack.c b/stack.c
--- a/stack.c
+++ b/stack.c
@@ -1,5 +1,8 @@
 /*
- * stack.c
+ * stack.c -- Stack implementation for RPN
+ *
+ * (c) 2005 Horst H. von Brand
+ * Licensed under the Open Software License version 2.1
  */
 
 #define N	8