9.  Key-pressed check
    ~~~~~~~~~~~~~~~~~
You can check to see if a specific key is being pressed at a particular
instant with a negative INKEY statement. For example, you can test the
space-bar with IF INKEY(-99) THEN...
However, if you want to see if ANY key is being pressed, (though not the red
keys or <Ctrl> or <Shift>), then use this command. It works in the opposite
sense to the other negative INKEY commands, hence the inclusion of the word
"NOT".     IF NOT INKEY(-129) THEN ...