That is how we allow you to restart at INTRO.2, INTRO.3 or DEMO_1.3 for
that matter!

NOTE that we have to account for both upper and lower case input, as we
do in the INTRO.BAT file, and here. at the top of DEMO_1.  The original
version of DEMO_1 dispensed with this requirement, and relied on the
"instructor" to remember to use lower case ... but the "bug" had to be
fixed in this version, as the "user" certainly would not know to try
lower case.

This illustrates just how easy it is to "mess up" if we do not plan
ahead for the user's "stupidity" ...  Murphy's Law reigns supreme!