When you ask SPELL to guess, it puts up a window for guess candidates, and
then goes away and tries to guess.  As it finds each candidate guess, SPELL
displays it in the window, labelled with a single (upper-case) letter.
Meanwhile, the `menu' at the bottom of the screen says "Guessing - please
make your selection".

SPELL expects you to select that one of its guesses that is correct; you
tell SPELL of your choice by typing the letter that labels your selection
(case not significant).  SPELL will then use your selected spelling to
replace the word that wasn't found in the dictionaries.

If you decide that the guessing process (which can take a long time) was a
bad idea, you may type <control-Z>, and guessing is abandoned.

If you hang on long enough, SPELL exhausts its guesses and updates the menu
to say "Guessing done - please make your selection".  If you still don't
like any of the candidates you may type <control-Z> at this stage, too.