Start off with Rook to a6 check. Pawn takes rook on a6. Black king moves to c6. White is forced to move his pawn on b4 to b5 checking the black king in the process. The king moves to c5. White's only move is pawn to b6. Black is forced to take the pawn with the pawn on a7 mating the white king.
this is very hard and it is a mate in four, post the answer once you get it!
this is a game that Rubinstien played against an amuatuer, but in this game, he demonstrated his amazing ability to mate!