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chess
This page is a list of personal notes on en passant. Specifically this is a list of situations to keep in mind for when considering a chess position's legality.
After black moves d5, white can recapture with e×d6.
After black moves d5+, white can recapture with e×d6. Note that the capture destination is not the same as the victim square, which you will need to take into account when recognising legality in your engine.
Clearly when the white pawn is pinned to the king, en passant is illegal.
Traversing a pin mask is legal.
En passant here is illegal, because that would expose the king to an attack from the rook on h5. The white pawn is effectively pinned in this position.
This situation is impossible. You can never end up in a situation where en passant is a valid move here, because white would already have been in check prior to black pushing her pawn two spaces. We can conclude there will never be a situation where the black pawn is pinned to the white king.