Request to Add Support for Turnover Chess Variant

[LucioFilho]

Hi Fairy-Stockfish team,

I'm Lúcio Filho, creator of Turnover Chess, a modern chess variant invented in 2018.

The variant features unique mechanics: pieces are composite stacks of up to three rings (Tower/T, Fort/F, Wall/W), which decompose on movement (only the outermost ring moves, leaving inner ones behind), and a powerful turnover capture where valid absorptions flip enemy rings to your color (like Reversi/Othello).

Key details:

• 8x8 board with asymmetric start (8 Castles each on first two ranks; White on dark squares, Black on light).
• Victory by eliminating opponent's Castles (no checkmate; stalemate loses).
• Promotion: Only Walls promote to Citadel on last rank.
• Playable with strong engine here: https://www.chessvariants.com/invention/turnover (implemented by H.G. Muller in interactive diagram).
• Full rules: https://www.turnoverchess.com/

The PlayStrategy.org team expressed interest ("looks like a great game and would fit nicely") and added it to their list, but noted that native Fairy-Stockfish support would greatly accelerate implementation in other platforms.

Given the existing robust implementation by H.G. Muller, adding a variants.ini entry (and possibly NNUE training later) seems feasible and would bring a fresh, tactical variant to platforms like Lichess forks, PyChess, and others using Fairy-Stockfish.

Thanks for maintaining this incredible engine – it's a game-changer for the variants world!

Best,
Lúcio
@TurnoverChess on X