Checkmate Patterns

This module is bigger than most because it isn't really one idea -- it's ten. Once a game actually reaches checkmate, the detector tries to name the shape of that mate against a library of classic patterns that have recurred often enough in real games to earn their own names. Recognizing the shape ahead of time is what lets a player spot a forced mate a few moves out instead of calculating from scratch every time; that's why this module spans such a wide difficulty range internally, even though the module as a whole is tagged "advanced" for its hardest content.

Some patterns are genuinely beginner material. Back-rank mate is the classic case: a king castled behind its own unmoved pawns gets mated by a rook or queen sliding down the open back rank, because its own pawns block every escape square. Smothered mate is almost as famous -- a knight delivers check to a king that's boxed in on every side by its own pieces, so there's no flight square anywhere, only a knight that can't be captured or blocked.

A cluster of patterns share a family resemblance: a rook or queen checks along the edge of the board while a second piece guards the flight squares a lone rook/queen couldn't cover alone. Arabian mate is the corner version, with a knight guarding the squares next to a cornered king. Anastasia's mate is the same idea one square off the corner, with the king pinned against the board edge between a knight and a rook covering the escape file. Anderssen's mate swaps the knight for a pawn doing the same guarding job. Damiano's mate is different in shape but the same spirit of teamwork: the queen mates right next to the king, kept safe from capture by a defending pawn.

The rest are their own distinct shapes. Boden's mate is two bishops on crossed diagonals -- one light-squared, one dark-squared -- slicing through a king that's boxed in by its own pawns. Ladder (or staircase) mate is two rooks (or a rook and queen) marching the king down the board one rank or file at a time until it runs out of room. Blackburne's mate pairs a knight delivering check with a bishop pair, one of which seals off the king's last flight square. Epaulette mate is visually distinctive: the king is still on its home rank, flanked on both sides by its own rooks like a soldier's epaulettes, mated by a frontal check straight down the file.

Any checkmate that doesn't match one of these ten specific shapes still gets recognized -- it just falls back to a generic "Checkmate" label rather than going unflagged. But the ten named patterns above are the ones worth burning into memory, because spotting the shape early is often the fastest route to finding the mating move.