The el-Mitra Exchange was a "classic attack" in the game of three-dimensional chess, used to counter the Kriskov Gambit. During a game of chess between Data and Deanna Troi, Troi employed the Kriskov Gambit, however, Data informed her that her attempt would be unsuccessful, if he countered with the el-Mitra Exchange, because he had already taken both of her rooks, which ultimately left her king vulnerable. (TNG: "Conundrum" )