Bought this to replace the copy that once graced the shelves of my old and long-gone chess library (350+ volumes). Smullyan's problems are very exacting and some understanding of the depthful process of "retrograde analysis" is required to comprehend the intention of the composer. Solvers must apply deductive reasoning to arrive at the correct solution and – like "normal" chess problems – there can be only one correct solution (unless, of course, there's a declared stipulation for multiple solutions). Often, the goal is to determine some relatively simple truth by examining the given position. The goal could, for example, be to reason out whose move it is by figuring out which piece was the last piece moved so as to determine whether White or Black made the last move. The diagrammed position must reveal all of this to the solver, given the application of the aforementioned deductive reasoning.
That said, how about an example of this genre? Not from Smullyan, but from Sam Loyd, who may be dubbed the "father" of retrograde analysis. Grab a chessboard and set up the following position: White pieces – K on e6, Q on a6. Black pieces – K on e8, R on a8, pawns on a7 and c7. This problem is as close as retrograde analysis gets to a "normal" problem. The stipulation to the solver is that it is White's turn to move and that he must checkmate Black in 2 moves. But Loyd expects the solver to ferret out the (recent) past history of this position predicated on the presumption that it leads back to the initial starting position and developed legally from there according to the rules of play. Once the solver accepts these conditions, the given position is seen to contain enough clues to answer the question of whether or not Black may castle, which would help him evade some of the more obvious checkmate attempts. To do this, the solver must ask what was Black's last move? The two black pawns are still on their original squares, which means that Black's last move was either with the king or rook. That, in either case, means castling is out of the question. Discovering that clue makes it easier to find White's moves 1. Qa1 and (after any reply by Black) 2. Qh8#. Despite the retrograde "twist," that was easy enough, yes?
Now let's go to the other extreme of difficulty. This retro problem by Gerd Wilts won first place in The Problemist 2004. It is a Proof Game in 18.5 moves. You see, chess moves come in pairs – White's move 1 followed by Black's move 1, White's move 2 followed by Black's move 2, etc. So right off, the solver will know that if the problem is 18.5 moves, the last move was White's 19th move. On your chessboard, set up the pieces thus: White pieces, Kh1, Qh3, Rg1, Rh7, Nf1, Nf3, Be3, and pawns on a2, a7, b2, d4, f4, and h2. Black pieces – Ke8, Qd8, Ra8, Rh8, Bf8, Nb8, Ng8, and pawns b7, c7, e7, and g7. Now look at this weird position. This is the sort of "impossible"-looking position that earned a paltry 2 stars from a previous reviewer. But in fact, it only "looks" impossible. This position can indeed be logically solved in terms of "Proof Game" stipulations, because there is no rule that requires players to make completely logical moves as if they were playing a game to win! The only requirement is that they make moves that are legal as per the rules of chess play. So here, the goal is to figure out the exact sequence of moves from the regular opening position to the present position by "retrograde analysis."
Without going into lurid detail, here is the actual gamescore. Set up the normal opening array and play out these moves to arrive at the given position. Then marvel at the genius it must take to figure all this out BACKWARDS! If you can do it, you're smarter than I am (which is not saying all that much)! 1.c4 d5 2.Qb3 Bd7 3.Qh3 Bb5 4.cxb5 d4 5.b6 d3 6.bxa7 dxe2 7.d4 f5 8.Be3 f4 9.Nd2 f3 10.Rc1 fxg2 11.f4 exf1(B) 12.Ngf3 g1(R) 13.Rc6 Rg5 14.Rh6 Ba6 15.Rxh7 Rb5 16.0-0 Rg5+ 17.Kh1 Rg1+ 18.Rxg1 Bf1 19.Nxf1
And there you have it! Obviously, neither imaginary player in this particular game is a sane person. However, the problem composer is a genius of the highest stripe! The object was to create the longest possible game, using legal moves (though not necessarily logical moves), all the while bearing in mind that one of the stipulations for creating a "Proof Game" requires that it be absolutely solvable by reasoning backwards (retrograde analysis) move-by-move until you reach the standard opening position! Dear reader, these are the sort of problems that confound the readers of Smullyan's "Chess Mysteries..." but once you realize that you are not being asked to solve an ordinary problem, but rather one that requires deeper dimensions of cogitation, you will acquire a keener sense of appreciation for the minds that compose such convoluted brain twisters! Good luck to you (though luck will have nothing to do with it).
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