"Stop him, Holmes! He's destroying the evidence." John Watson, MD hurled himself at the seated figure of Professor Moriarty. Alas, too slowly, for by the time he made contact with his adversary, the professor had swallowed both scoresheets.

Sherlock Holmes, playing White against Moriarty in the Reichenbach Falls championship final, was unperturbed. He calmly removed the black g-pawn, and moved his pawn from h5 to g6.

Moriarty shook his head in disapproval. "The en passant capture," he said, "is valid only if my last move was a pawn advance from g7 to g5. Can you prove it?"

"He's right, Holmes," Watson interrupted. "Without scoresheets, I fear the task is beyond you."

"I think not," said the great detective. "Examine the formation on the Q-side. Black's pawn captures account for every missing white man; the white pawn cannot have reached b4 until after a black pawn captured from b4 to a3, and the white Q-rook cannot have escaped until after b4 was played. The sequence of events must thus have been: b4xa3, b4, rook sidles in to a4 via a5, and finally Kb5-a5. And that final move must have been made in reply to d7xc6+, which in turn must have been played before bishop and rook emerged from c8 and a8. But both those pieces must have been taken by White's pawns on the K-side. There is only one way to retract the last few moves: Black has just played 1...g7-g5, preceded by White's g5xRh6, then Rd6-h6, g4-g5, Rd8-d6, f3xBg4, 0-0-0, f2-f3, Bc8-g4, Kb5- a5, dxc6+."

"Why cannot my last move have been g6-g5?" asked Moriarty.

"For then," explained Holmes, "we retract g6-g5, g5xRh6, g7-g6, g4-g5, Rd6-h6, f3xBg4, Rd8-d6, f2-f3, 0-0-0 and White is in retro-stalemate - he has no possible previous move." he looked up and saw Moriarty choking as he tried to eat the white g-pawn.

"My game, I think," Holmes said as Moriarty was carried off.

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