Checkmate in 1, not that hard though

If we need to consider every possibility that gives a mate in one then KieferSmith already found it (currently post #10).

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.)

OK, then what rule does en passant violate? A chess move (or position) is illegal if it violates a rule of chess. Which rule does this en passant violate?

The FIDE rules for chess are not that extensive. There aren't that many. Which of those rules is violated by the move en passant? I understand you can't prove what the last move was, so what. Most chess positions are ones where the last move cannot be proven.

Since there is no evidence, no proof, that c7-c5 WASNT played then it must be considered.

Negative. It was a little confusing because it said mate in one. It should have said mate in two. There is a mate, just not in one. Presenting pieces that do not exist is not a possibility. That would violate several rules of chess and make the position (and move) illegal.

The answer to this is obvious, and I already told you anyway. It violates the en passant rule. (What else?)

I don't feel that this discussion leads anywhere.

This is the rule for en passant. How, SPECIFICALLY does either the move c7-c5 or the ensuing en passant capture violate the en passant rule? I'm curious, because I just don't see it. I assume you mean there is no proof that c7-c5 happened. Well there is no proof c6-c5 happened either. There is no proof en passant ISN"T possible. So what rule is violated. Specifically.

3.7 a. The pawn may move forward to the unoccupied square immediately in front of it on 
the same file, or
b. on its first move the pawn may move as in 3.7.a or alternatively it may advance two 
squares along the same file provided both squares are unoccupied, or
c. the pawn may move to a square occupied by an opponent’s piece, which is 
diagonally in front of it on an adjacent file, capturing that piece.
d. A pawn attacking a square crossed by an opponent’s pawn which has advanced two 
squares in one move from its original square may capture this opponent’s pawn as 
though the latter had been moved only one square. This capture is only legal on the 
move following this advance and is called an ‘en passant’ capture

This part: "This capture is only legal on the move following this advance"

As I said, in chess compositions there is an agreement that e.p. is illegal unless it is proven that it's not. This puzzle would be thrown out from any competition.

It would work as a chess-com puzzle as those show the last move. But without showing the last move it's simply wrong.

Well I certainly didn't agree to any such thing. And this isnt a competition. For all we know this is from an actual game. I'm simply using the information, the position, given. I don't have any proof c7-c5 wasn't the last move. Do you?

There is nothing to suggest the previous move was NOT c7-c5, so there is nothing "illegal" about capturing en passant since no rule is violated.

The challenge here is to find the checkmate. In post #8 I said it's mate, but not in one. I didn't want to say two as that probably would have made it too easy. So given it's a mate in two, what other possible LEGAL moves could be the answer? c6-c5 is a legal move, but it doesn't provide any opportunity for capture. Unless I'm missing something, capturing en passant is the ONLY way to achieve a mate in two.

How's an ifridge work?

First of all: whose opinion is valued more: the professional puzzle-creating community, or one random 1800's opinion? (Spoiler: it's not you)

You're using just the information given to you? In that case, from the information I have about Charles Lindbergh, Jr, I don't have any proof that the Lindbergh baby was killed by the one-year-old Jim Jones under the combined orders of the Freemasons, the Illuminati, the CIA, and John Cena's grandparents.

The rest of your argument basically sums to "I said it, the puzzle's creator, a barely reliable source rated 700 in rapid, said something similar but distinct and also factually incorrect, so therefore it must be true." In that case, since I believe that atom bombs are safe, and Mao Zedong said that they aren't dangerous, then atom bombs must be safe.

You seem to continuously be ignoring the line where @magipi writes, "e.p. is illegal unless it is proven that it's not." Perhaps it's because you know that your argument relies around this being false? Or maybe you just don't know what e.p. stands for. Honestly, at this point, I can't tell.

In fact if it's been posted from a game it's been set up with no e.p. anyway.

I agree the puzzle creator, whether from a real game or not, is incorrect. I corrected it. It's not a mate in one. It's a mate, but not in one. It's a mate in two. As others said later, he probably didn't consider the bishop that adds one move.

Some people may have the opinion that "e.p. is illegal until it's proven that it's not". But that's not what the rules say. The rules of chess, which I posted, do not prevent en passant in this case. The rules say nothing about proving the previous move nor do they say anything about saying it's an "illegal" move until proven otherwise. The previous move had to be c7-c5 for en passant to be a valid move. And that was the previous move, so it's a valid move. How do I know? Because it's a mate in two. (not one). No other previous move by black allows a mate in two. None.

So I see only two options. Either it's NOT a mate in two (which would probably defeat the whole purpose of posting the position and doesn't really make any sense) or c7-c5 was the last move before this position. Do you see a third option for this position?

This would be a similar example. If I said "mate in one" I don't need to prove the previous move. I don't need to prove my king or h rook haven't moved. Everyone knows they haven't moved because it's a mate in one. The ONLY way it's a mate in one is if they haven't moved. Castling is legal because it's a mate in one.

The statement provides all the proof anyone needs. In the case of the original position posted here, just ask the OP if c7-c5 was the previous move. If he says no, they I would agree an en passant capture would be illegal. But if he says yes, would that be enough "proof" that en passant is a legal move?

54. PxP e.p. Bd4

55. BxB#

By the way, this is not how chess notation works. It's worth learning notation, it only takes like 10 minutes.

It's close enough for me. And we all value different things. What might be worth something to you could be worthless to someone else. I doubt there is anyone who doesn't understand it. It would be like saying I live in america.

I know that's not how grammar works, but everyone still understands what it means.

There is only one answer. Being that it's a mate in two. There is no answer for a mate in one.

Actually, it's hard to read. This is the equivalent of someone writing a mess of capital and lower case letters. Or someone switching to roman numerals in the middle of a math equation and back again.

But sure, I can decyipher what you mean.

Then how would it be a mate (the title in the topic) if c7-c5 was NOT made? Yes, I assume that was the last move because of the huge letters describing the topic. That is my indication. But if you need even more clarity, ask him. Ask the OP what the previous move was. Go on, do it. The worst that could happen is that he says no. In that case, you would be right, there would be no mate at all.

In the example I gave would you just assume either the king or the h rook has moved? If I titled it "mate in one" is that not enough indication for you that castling is a legal move?

I don't know about you, but over time I've had the opportunity to play chess against people that are not very good. Sometimes, they are even bad at the game of chess. They make mistakes. They blunder, they don't see certain moves. They sometimes don't even see mate in ones. Or easy captures.

The fact that you and I would BOTH make far different moves and consider this position senseless does not detract from the fact there are a LOT (and I mean a LOT) of people who are not as good as you and I.

So, imagine a chess player who is not very good. Now, imagine he or she is under extreme time pressure. There is a high probability that this low rated player who makes huge mistakes very often will end up with positions that you and I would consider "senseless".

What if this low rated player sees one, and only one move? Immediate check. They move the bishop from h2 to g1. (believe me I've seen beginners make worse moves). Now it's blacks turn. But they can't figure out at first where to move. Finally they stumble on to the only legal move. c7-c5. Now the other beginner has a stroke of brilliance. Take the pawn ep!! which results in check again. And what if this is maybe the beginner's best game to date that he's ever played? He might be quite proud of it. The fact that mate is delayed a move by the black bishop probably isn't that important. Mate in two instead of one. We all make mistakes.

So there is only one previous move that matters. c7-c5. Anything prior to that could be anything, for any reason. Beginners make moves you and I would never suspect. So the most reasonable and logical assumption is c7-c5 because of the glaring title of this topic. There is no other previous move that results in mate. If there is, what would you suggest the alternative previous move was?