diff --git a/frustration.rs b/frustration.rs
index 57da3d9..fecdc75 100644
--- a/frustration.rs
+++ b/frustration.rs
@@ -46,9 +46,20 @@ use std::convert::TryInto;
  * But before we can do any of that we will need a machine.  Let's make one.
  */
 
+/* Table of Contents
+ *      Part 1 - The Computer
+ *          Part 1a - The instruction set
+
+ *      Part 2 - The Program
+ *          Part 2a - The lexer
+ *          Part 2b - The outer interpreter
+
+ *      Part 3 - Using the interactive programming environment
+ */
+
 /* ---------------------------------------------------------------------------
  *                           Part 1 - The Computer
- *  ------------------------------------------------------------------------ */
+ * ------------------------------------------------------------------------- */
 
 /* This computer will have a 16-bit CPU.  It will be able to access
  * 2^16 (65536) memory locations, numbered 0 to 65535.
@@ -187,6 +198,10 @@ fn new_core() -> Core {
     return c;
 }
 
+/* ---------------------------------------------------------------------------
+ * Part 1a - The instruction set
+ * ------------------------------------------------------------------------- */
+
 /* Now we have a CPU sitting there but it does nothing.
  *
  * A working CPU would execute a list of instructions.  An instruction is
@@ -640,7 +655,7 @@ const PRIMITIVES: [Primitive; 16] = [
 
 /* ---------------------------------------------------------------------------
  *                            Part 2 - The Program
- *  ------------------------------------------------------------------------ */
+ * ------------------------------------------------------------------------- */
 
 /* You now have an unfamiliar computer with no software.  Can you and the
  * computer write a program?
@@ -1205,7 +1220,7 @@ fn build_dictionary(c: &mut Core) {
      */
 
     /* -----------------------------------------------------------------------
-     * Part 2a. The lexer
+     * Part 2a - The lexer
      *---------------------------------------------------------------------- */
 
     /* Now that we've got some basics in place let's go back to solving
@@ -1767,7 +1782,7 @@ fn build_dictionary(c: &mut Core) {
     forth!(word, find, RET);
 
     /* -----------------------------------------------------------------------
-     * Part 2b. The outer interpreter
+     * Part 2b - The outer interpreter
      *---------------------------------------------------------------------- */
 
     /* We can now look up a subroutine in the dictionary by typing its name
@@ -2192,6 +2207,10 @@ fn main() {
     }
 }
 
+/* ---------------------------------------------------------------------------
+ *           Part 3 - Using the interactive programming environment
+ * ------------------------------------------------------------------------- */
+
 /* "The next step is a problem-oriented-language. By permitting
  * the program to dynamically modify its control language, we
  * mark a qualitative change in capability. We also change our