  We discuss games involving a counterfeit coin. Given one counterfeit coin
among a number of otherwise identical coins, two players with full knowledge of
the fake coin take turns weighing coins on a two-pan scale, under the condition
that on every turn they reveal some information to an Observer with limited
prior knowledge about the coins. We study several games depending on the types
of the counterfeit coin, the end-game condition, and the availability of extra
genuine coins. We present the winning positions and the Grundy numbers for
these games.
