pattern symbols

M	a known mine
0-8	a square with this number in it
-	a square known not to be a mine
+	a known square of any sort
?	an unexplored square
*	any square
a-z	a square with a number in it, and the number is remembered
|	a square off the board

NOTE: You do not need to create separate rules for symmetric patterns;
the system will automatically try each rule in every possible rotation and reflection.

scheme variables

star-mine-count	number of known mines matched by stars
star-unknown-count	number of ?'s matched by stars
a, b, c, etc...	number matched by the given letter
a-mine-count, b-mine-count, etc...	number of known mines surrounding the given letter