Clicking analysis reveals that en passant is not alegal move, so that is not correct.
Why isn't en passant a legal move? It's still checkmate, just not in one.
En passant is only legal if black's last move was c7-c5. There's no proof that this would be the case here. Therefore e.p. is not legal.
I wouldn't say that makes it illegal. I would say it makes it the ONLY possible move given the conditions of imminent checkmate. I don't see anything in the puzzle that prevents the move c7-c5, or anything that indicates an illegal position or illegal moves. In chess, an illegal move is one that violates the rules of chess. Which rule of chess does the move c7-c5 (or the ensuing en passant) violate?
Read again what I said. I never said that c7-c5 is illegal. En passant is illegal, because it is only legal after precisely c7-c5, and there is no indication or proof that this would be the case.
In chess compositions, there is an agreement that e.p. is illegal unless it is proven that it's not. (Bizarrely, castling is the opposite.)
Clicking analysis reveals that en passant is not alegal move, so that is not correct.
Why isn't en passant a legal move? It's still checkmate, just not in one.
En passant is only legal if black's last move was c7-c5. There's no proof that this would be the case here. Therefore e.p. is not legal.
I wouldn't say that makes it illegal. I would say it makes it the ONLY possible move given the conditions of imminent checkmate. I don't see anything in the puzzle that prevents the move c7-c5, or anything that indicates an illegal position or illegal moves. In chess, an illegal move is one that violates the rules of chess. Which rule of chess does the move c7-c5 (or the ensuing en passant) violate?
I'm sure we could take a billion three hundred million trillion three hundred million positions where there was no proof of what the last move was. That doesn't make them illegal.
I would say that every possible legal move must be considered, and since there is no proof that pawn move WASNT played it must be considered as well.
If we need to consider every possibility that gives a mate in one then KieferSmith already found it (currently post #10).