The -size parameter sets the overall board size. This must be an even
number in the range 5..31 (the default being 15).
Is this a new meaning for "even"?
No, that was a cut & paste error. Many thanks for pointing that out.
I might stick with convention and use the traditional meaning of "even".
Redefining it probably wouldn't be worth the effort (rewriting every
dictionary, math text, school syllabi, etc ever written) just for this game.