alt Hacker News> Chess is a lot trickier than it looks. It has so many rules: castling, en passant, pawn promotion, pinning, the discovered check, and the deadlock case of stalemate.
Nit: Pinning and the discovered check are not really rules, but rather names of tactics.
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juujian • today at 12:18 PM
And discovered check means that it is not sufficient to check the position of the piece you have moved, you also need to check the position of other pieces to see whether there is a new check.
Well, if a piece is pinned it's illegal to move it.
Rule 3.9.2: No piece can be moved that will either expose the king of the same colour to check or leave that king in check.