[Event "Arabian Knights"] [Site "?"] [Date "1981.??.??"] [Round "?"] [White "Raymond Smullyan"] [Black "?"] [Result "*"] [WhiteFideId "-1"] [BlackFideId "-1"] [Variant "illegal"] [SetUp "1"] [FEN "8/8/8/1r1b4/B7/8/8/3k4 b - - 0 1"] [PlyCount "0"] [GameId "2261180231012369"] [EventDate "1981.??.??"] [SourceVersionDate "2025.12.15"] {The white king is invisible. Where is it? To find the only possible solution, one must first try to find out whose move it is, White or Black's. The next question is under what circumstances can a king can be in check by two different pieces. From there it is a small step to find the few moves that must have preceded the diagrammed position and indicate the spot where the white king stands. The solution can be found on many internet sites, for instance here: https://chess.stackexchange.com/questions/23538/how-does-one-know-if-a-position-is-not-reachable-from-a-series-of-legal-moves-fr/23544#23544} *