jeff@heurikon.UUCP (02/28/84)
Original posting: ---------------------------------------------------------------------- This is my all time favorite chess problem. Unlike most "mate in two" puzzles, this one is unlikely to occur in a game. But it *is* possible to get to this position, and knowing that is the key to the solution. This isn't an ordinary chess problem since the solution requires a fair amount of inductive reasoning. Black (lower case) .-----------------. | - * - * k * - * | Part 1: White to play and mate in two. | * p * - P - * p | | - * N * P * N * | Part 2: At first blush there appear to be | * - P p K p P - | two possible solutions. Prove that | - * - P p P - * | there can be only one. | * - * - P - * - | | - * - * P * - * | Solution: see below... | * - * - * - * - | `-----------------' White (Caps) Caution: Don't confuse the "P"s and the "p"s. White is moving up ^, Black is coming down. ---------------------------------------------------------------------- Solution: 1) P(N5)xP (en passant) ... 2) P-B7 mate Reasoning: Black's last move had to be either P-B4 or P-Q4. There are no other previous legal positions for Black to have been in. The black King could not have just moved into its present position, else Black would have been in check for more than one move (The whilte pawns in the area couldn't have just got there). Similarly, the other black pawns are trapped and could not have just moved. Neither of the two black pawns could have just come from Black's 3rd rank. If Black had had a pawn on B3 or Q3, White would have been in check when Black played P-[BQ]4, which makes no sense. The position would have been illegal. Thus, the pawn started from B2 (or Q2), giving White the option of capturing en passant. Furthermore, Black's previous move could *only* have been P-B4. If you count the number of captures which the white pawns have made, you get 10. That accounts for all of Black's losses. Thus, Black's QB had to have left the back rank under its own power to meet with its destiny. Black's KP, therefore, must have moved out of the Bishop's way some time ago. That leaves P-B4 as the only posible previous move. Trickyyyyy, huh? I love it! Only two people, that I'm aware of at this time, got it (ihnp4!ihuxe!rainbow and ihnp4!astrovax!fisher!djl), but there could be others down deep in the net... -- /"""\ Jeffrey Mattox, Heurikon Corp, Madison, WI |O.O| {harpo, hao, philabs}!seismo!uwvax!heurikon!jeff (news & mail) \_=_/ ihnp4!heurikon!jeff (mail - fast)