Very hard mate in 1

@a_pleasant_illusion How would dxe6 ep help? That doesn't lead to a faster checkmate, unless I'm missing something.... Never mind, I'm an idiot.

You're missing the bishop on b2

Aren't en passant rights meant to be part of the FEN?

@mCoombes314

Yes, and is why I said in my original post that not all the flags were set. The FEN should indicate en passant when it is legal.

I'm guessing the OP excluded it on purpose, to prevent the hordes of people who would just immediately open the position,run the engine, and shout out the solution in the forum, but it's still a little shady :)

I understand why OP excluded the flag, but it makes it impossible to execute the mate. I didn't use the computer, and since en passant was "illegal" it was impossible to test out. Good puzzle, but could have been clearer. Excluding crucial information just because some people will use a computer to solve the puzzle is odd: by that logic no puzzles should exist anymore.

I'd be okay with this puzzle if any other move than e7-e5 also led to mate in 1

Ok, forget this epic ep! ;)

White to move, #1

lichess.org/editor/1Bb3BN/R2Pk2r/1Q5B/4q2R/2bN4/4Q1BK/1p6/1bq1R1rb

WOW @Sarg0n.... so many 'maybes" but only one right answer. Nice.

@mCoombes314

I agree. This is why I said it's still a little shady :)

It's a bit easier to reason out this sort of position where the only thing missing is an en passant flag; when you realize nothing normal is a mate in 1, you ask yourself what would have to be true for a mate in 1 to exist. Here there's a very small change, the addition of legal en passant on e6.

It's not so tough in this case, as the fact that a couple people figured it out fairly quickly indicates :)

With more "normal" puzzles, though, it's much harder to obscure the position in such a way that meets both criteria:

1) Humans can easily reason out the obscured information (i.e., it's a minimal thing, like an en passant flag)

2) Engines won't solve the puzzle.

Either way, I'm not saying this is a perfectly reasonable way to present puzzles; it's definitely a trick :)

I take back what i said about this problem, its brilliant. This does actually work as a retrograde problem. White last move must have been Bb2+, black must player either e7-e5 or f6 both which lead to mate in 1, we only have 1 variation but we can work out the other working backwards from the position, brilliant stuff!