- * To at least _try_ to avoid boring cases, check that
- * this move doesn't directly undo the previous one, or
- * repeat it so many times as to turn it into fewer
- * moves.
+ * To at least _try_ to avoid boring cases, check
+ * that this move doesn't directly undo a previous
+ * one, or repeat it so many times as to turn it
+ * into fewer moves in the opposite direction. (For
+ * example, in a row of length 4, we're allowed to
+ * move it the same way twice, but not three
+ * times.)
+ *
+ * We track this for each individual row/column,
+ * and clear all the counters as soon as a
+ * perpendicular move is made. This isn't perfect
+ * (it _can't_ guaranteeably be perfect - there
+ * will always come a move count beyond which a
+ * shorter solution will be possible than the one
+ * which constructed the position) but it should
+ * sort out all the obvious cases.