Notes On the Code Illustrations

For clarity of presentation, I have broken our code into many discrete subroutines. For the purposes of discussion you can assume that all variables are global in scope (even though this is obviously not the case in our program). Some blocks of code which add little to the illustration have been replaced with a place holder comment such as '<Error trap>.

Some code fragments have been simplified and turned into sub routines for clarity. In this process some inconsistencies may have been introduced.