The Last Match Loses
Two piles of matchsticks. Each turn you take as many as you like from one pile, and whoever takes the last match loses. Match the positions that are already lost for the player about to move.
Each pile is a run of 1s and the two piles are separated by a hash. An empty pile is an empty run, so "1#" is one match and none, and "#" is no matches at all. With the ordinary rule — last match wins — two-pile Nim is solved in a line: you are lost exactly when the piles are equal, because whatever you take, your opponent takes the same from the other side. The misère rule keeps that answer nearly everywhere and breaks it right at the bottom of the board, where copying stops being safe. Find the exceptions. There are not many, and they are not where you expect.
11#11must matchtwo and two
1#must matchone and none — you must take it
#1must matchand the same the other way round
1#1must not matchone each: take yours and they are forced to take the last
#must not matchnothing left, so they took the last match and you have won
11#111must not matchtwo and three
11#must not matchtwo and none
+ 10 hidden tests, checked when you submit. They are what stops a pattern that only fits the examples above.