Yes, and I think your new problem is possibly a good stab at transforming this one. I guess I should stop falling for what could be trolling on here that tries to lead us back to the original problem then. It just keeps being hard for me to tell if people are seriously trying to answer en passant and don't understand (because this topic can actually be pretty dense) or they are trolling to try to get a rise out of people.
The Hardest Mate in 1 ever.
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Where it is hard to tell ignorance from trolling, the ignorance is probably so great that it is best to treat it the same way. When someone is ignorant but eager to learn, he will reach out at some point with a message that makes some sense and contains a question mark. Then it is time to respond seriously, IMO.
Hm... we should have had you here the last time this went around. Thanks.
n9531l1 wrote:
@Arisktotle: I'm confused by the moves shown at #85. Where was the white king when Black played f4+? Where was the black king when White played Ng5+? Have I misunderstood what these moves represent?
I assume you looked at the move notation and found it hard to visualize the retractions with your minds eye. You don't need to. Clicking on the back arrow 5 times will take the diagram 5 plies back in time. Next you can step through the moves with the forward arrow. This will answer all your questions!
When I started composing retro problems I habitually confused normal chess moves with retraction moves. After about 2 years of mixups the air cleared in my head. Since that time I can play forward and backward chess and switch between the two without effort. Very useful for composing and solving retro problems!
@Arisktotle: I had to back #85 up several more moves to see how the given moves were even possible. Could you explain in a few paragraphs what the procedure is for constructing a position like this? (Posted after I deleted my previous post and before I saw your reply to it.)
n9531l1 wrote:
@Arisktotle: I had to back #85 up several more moves to see how the given moves were even possible. Could you explain in a few paragraphs what the procedure is for constructing a position like this?
(Also see my previous post) I have no standard article for that and writing it will take some time. Generally, you should never start retracting until you have done some preliminary structural analysis which will yield you the boundary conditions for the do's and dont's of retracting. I left that part out of my solution comments because it's a pretty boring story with the same items in every analysis: explaining the pawn structure, the pawn captures and the promotions. Including the alternative histories and the free captures (not required for pawn structure explanation) associated with each history. More some other time.
Arisktotle wrote:
n9531l1 wrote:
@Arisktotle: I'm confused by the moves shown at #85. Where was the white king when Black played f4+? Where was the black king when White played Ng5+? Have I misunderstood what these moves represent?
I assume you looked at the move notation and found it hard to visualize the retractions with your minds eye ...
Addendum: The move notations shown with diagrams by the game and puzzle interfaces of chess.com fall short when identifying retraction moves. This is explained by my last post of 2 days ago in the puzzle topic "Z42 Chess Puzzle #1". A chess move is not the same as the notation of a chess move. Correct retraction is only possible with reversible algebraic notation and it is not available on chess.com. Scrolling through the moves with the diagram navigation arrows though is sufficient as it equates to playing the camera recordings of my post.
(I am aware you deleted the post but the subject is of great significance 
)
Apr 28, 2019
0
#89
a random boi has entered but I am pink sheep the greatest sheep of all time so do not disrespect me you pieces of star lord I need my milk though bye har har u are wasting your time reading this I don't care what rules the forum has pink sheep has entered bye this aint the last of me
Easy
Cool
Easy
Uncheck the follow box under the bottom right corner of the comment box, that should work.
Easy
Hint:en passant
Hint:en passant
markgwen123456 wrote:
Easy
Hint:en passant
Hint:en passant
Prove that Black's last move must have been e7-e5. I don't see a way to prove it since e6-e5 is also possible.
If the position is like this,
then yes, the previous pair of half-moves must have been 1...e5 2. fxe5+, since there is no other way the Black king can be under the double check. But the position in the original puzzle could have come from e6-e5 as well.
Note that there is a difference between these two.
The above is a mate in one after Black's move.
This is not a mate in one because we are uncertain of Black's last move, just as we cannot cross multiply the denominator in inequality problems if we are uncertain of whether the denominator is positive or negative.
eric0022 wrote:
............................. This is not a mate in one because we are uncertain of Black's last move, just as we cannot cross multiply the denominator in inequality problems if we are uncertain of whether the denominator is positive or negative.
From the axioms of chess it in indeed impossible to conclude whether or not white can capture e.p. . However, uncertainty in itself does not count as a decisive argument, since there are supplemental conventions providing default conditions for uncertain states. For instance, you cannot prove castling right either, but the conventions do permit you to castle unless castling right can be disproved. It's all a matter of consensus.
Yes, but you know those supplemental conventions don't let you play en passant in this position (why are you muddying up an already muddy topic?) People can look at the conventions in a couple of way... 1. You're just not allowed to assume any moves were made without proof. (castling is assumed legal because you can't prove the King or Rook moved, en passant is assumed illegal because you can't prove the pawn just moved.) 2. Imagine the conventions worked some other way, what would this mean for chess composition? The answer is castling problems would not work and this kind of joke of a puzzle would be just about the only kind of e.p. problem possible to construct because it's so hard to prove a negative. Q: What conventions would allow for richer chess composition? A: The ones we already have. So why are we trying to reinvent the wheel with this puzzle? 3. People keep saying if you are ignorant of the conventions or you are allowed not to apply them then there is no problem with the puzzle as a simple logic problem. There is; this puzzle actually begs the question if you do that, ("well yes, obviously it's possible to satisfy the stipulation... unless it isn't.") but idk, trying to explain that to people is dangerous; I still remember the last time I had an argument about it in the context of this puzzle.
My comment was not on the puzzle or its history or on the (absent) right to play e.p. but only on eric0022 's argument in his previous post. He suggested that uncertainty was the reason for not allowing e.p. - see his reference to inequality problems - but that is insufficient as uncertainty can also lead to the opposite outcome. It is uncertainty coupled to the e.p. convention that causes denial of the right to capture en passant. It is quite possible that eric0022 is aware of that, but I thought I'd better clarify it for those who never heard of retrograde conventions.
en passant