actions.
(On Mac OS X, to conform with local user interface standards, these
-actions are situated on the \I{File menu}\q{File} and \q{Edit
+actions are situated on the \I{File menu}\q{File} and \I{Edit
menu}\q{Edit} menus instead.)
\dt \ii\e{New game} (\q{N}, Ctrl+\q{N})
will be a square you can fill in with a single number at all times,
whereas at \q{Intermediate} level and beyond you will have to make
partial deductions about the \e{set} of squares a number could be in
-(or the set of numbers that could be in a square). None of the
-difficulty levels generated by this program ever requires making a
-guess and backtracking if it turns out to be wrong.
+(or the set of numbers that could be in a square). At
+\q{Unreasonable} level, even this is not enough, and you will
+eventually have to make a guess, and then backtrack if it turns out
+to be wrong.
Generating difficult puzzles is itself difficult: if you select
\q{Intermediate} or \q{Advanced} difficulty, Solo may have to make
\b \cq{da} for Advanced difficulty level
+\b \cq{du} for Unreasonable difficulty level
+
So, for example, you can make Solo generate asymmetric 3x4 grids by
running \cq{solo 3x4a}, or 4-way rotationally symmetric 2x3 grids by
running \cq{solo 2x3r4}, or \q{Advanced}-level 2x3 grids by running