$100 Theme

The $100 Theme is a currently unachieved theme in chess helpmates. It consists of a double Excelsior promotion to knight in a helpmate-in-five. That is, Black and White cooperate to checkmate Black, with Black (viz. White) moving a pawn from the seventh (second) rank to the first (eighth) rank and promoting to knight, with White's promotion giving checkmate. As of January 2022, this theme has never been achieved in a sound helpmate-in-five with no promoted pieces.

History

This theme originates from 1963.

TODO: Explain naming

Difficulty

According to Keym (2005), there are two main difficulties when attempting to achieve the $100 Theme in a sound composition, both relating to eliminating duals.

The first is to justify why the black pawn must make a double step and not a single step on its first move.

The second is to justify why the black pawn must promote to a knight. This is often done by having both pawns promote on the same file, and having the black pawn promote on the same diagonal as the white king. A promotion to bishop or queen would thus be check (disallowing White from promoting to knight), and a promotion to rook would cover the white pawn's promotion square (allowing Black to capture the newly-promoted white knight, preventing the mate).

Examples

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References

TODO: Add the following references where necessary.

Vladimirov's "1000 adventures on the chessboard" (ISBN 978-5-271-15843-8)

Other citations: articles by Hans Gruber in feenschach (issue 95, 1990; issue 106, 1992; issue 156, 2003) - http://problem64.beda.cz/silo/feenschach95_1990.pdf - http://problem64.beda.cz/silo/feenschach106_1992.pdf

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