Chess has surprisingly rich rules, so it’s useful to model it as a concurrent system and ask which safety invariants always hold. The post distinguishes state invariants from transition invariants, then walks through examples such as turn parity, king safety, move-count growth, and square-change constraints. It also tests how those invariants survive rule additions like castling, en passant, and pawn promotion. [muratbuffalo.blogspot.com]
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