The Hardest Mate in 1 ever.

Oh right... nevermind then.

He mentioned it when he started this thread... But as some people, including me, had decided that it's impossible task... one move mate... they begun to suppose other solutions with two moves mate.

Here is a variant that works! It is standard chess + the Madrasi condition. Madrasi means that units of the same type (Q, R, B, N, P but not K) attacking each other, freeze one another. Example in the diagram: Rb8 and Rb7 are frozen. They cannot play again or give check until one of them is captured by another type piece.

White mates in 1 in the diagram - which is legal and could occur in a regular chess game played with or without the Madrasi condition.

Solution in white characters (highlight to see):

[[ 1. dxe6 e.p. #  The en passant move is legal because the white king is in check and e7-e5 is the only legal last move. The reason is that any other last move would be illegal because it violates the Madrasi freeze condition e.g. Qb6-d8+ or Re7-e8+. Note that the en passant move freezes Qd8 by Qd1. Also note that 1 ... f7-f6 is illegal because Pf7 is frozen by Pe6 and not because Rb7 checks the king - Madrasi. ]]

Did not find it. But as it happens this position is effectively impossible to reach in game, I don't feel so bad anymore.

It's standard chess but with an extra rule, Madrasi, which is explained in my previous post. After dxe6 e.p., the queen on d1 and the queen on d8 attack ech other and are therefore paralyzed (frozen). That disables the check of the black queen.

With standard chess rules, it is very difficult to prove the right to play an e.p. move but it is considerably easier with the help of the Madrasi device.

Found it! (highlight for answer)


1. c8=R ... d4
2. Nc7#

c8=Q d4 Qb7#

@Arisktotle Nice one! I'm just surprised you'd post a position involving unorthodox rules when some people here don't even comprehend the orthodox problem rules.  One question though - many of the units in your problem seem unneeded and I was wondering why you added them? 

Thx! I tried to stay as close as possible to the original post in this thread and also paid some attention to making the diagram "just legal". Not so easy to see how it could come about in a chess game played with the Madrasi condition.

It is possible to show this idea in a version without the 2 ugly white queens but the position would then look very different.

I am familiar with the combination of fairy chess with retrograde analysis and it is becoming increasingly popular amongst retro composers. I favor the viewpoint that one should assume that the proof games are played by the same rules as indicated in the problem stipulation.

it is easy pawn takes on e6

STOP REVEALING WHITE TEXT!!! NOW DELETE THAT POST!!!

Mate in 3.

I see mate in 2 with Rf7+, Kh1, Qf6#

Oopses! I edited it!

Is this mate in 1 or is it mate in 2 ? Prove your answer by analyzing the moves preceding the diagram! Standard chess rules and conventions apply as explained by Rocky64 in post #43.

Neither!

Okay, that makes sense! Yes, I agree with that idea about the legality of fairy problem positions.

It's mate in 1 with dxe6 e.p. because ...e7-e5+ is the ONLY possible last move. The WK is in check by the e5-P, which has 3 potential last moves, ...f6xe5/e6-e5/e7-e5+. To rule out the first 2 options, we need to do some retro-analysis. First, a piece count: White is missing the a-P only and Black is missing Q, light-squared B, and P. Black's doubled e-Ps are too far away from the a-file for White's a-P to have reached the e-file directly; instead the a-P must have promoted, either to be captured on the e-file or to replace a white piece that was captured. Since Black's a7-P is still on its original file, White's a-P must have captured at least once to promote, and this plus the doubled f-Ps account for 2 of the 3 missing Black units; so there's only 1 spare black unit that could be captured elsewhere.

How did Black's P on e2 get behind the white one on e3? Suppose this e2-P was the original e-P and it marched straight down the file; this would require White's original d- and e-Ps to "cross-capture" and swap files to let the BP through, but this is impossible because there's only 1 spare black unit to capture. Therefore the e2-P came from an adjacent file, capturing directly on e2. That means the e5-P was Black's original e-P, and without spare white units to capture, Black's last move could not have been ...f6xe5+.

Whether Black's last move was ...e6-e5+ or ...e7-e5+, White's previous move was a check given by the d4-B. This check was either Bc3xd4+ (due to the blocking Ps on c5/e3) or Ke5-f4+. Suppose the former - what could the WB have captured on d4? Not the missing Q because it would be giving an impossible check to the WK (e.g. ...Qf6-d4+?? already checking White from f6, or ...Qa4xd4+?? but no spare white unit to capture). Not the light-squared B since d4 is a dark square. And not a P because on d4 this BP and the WP on d5 couldn't have gotten around each other. That leaves Ke5-f4+ as the only possibility, but on e5 the WK would have been in check by the d7-N. The BN delivered that check with ...Nf6-d7+ (or Nf8-d7+), and prior to that, the WR on b7 may or may not have been checking the BK, depending on whether Black's last move in the diagram was ...e6-e5+ or ...e7-e5+.

Consider the former, ...e6-e5+, meaning the WR was checking the BK. How did the WR deliver that check, when there are blocking pieces on b8 and b6? Here's the crucial position.

Only a discovered check could have worked, and there are 3 options. Nf7-g5+ means the WK was in check by the h5-R, but Black had no way of making that check. Similarly, Nf7-d6+ means the b8-B was giving an impossible check to the WK. The third option is c7-c8=Q+. This means White's a-P had made 2 captures, a5xb6xc7 (to get behind the c6-P), and this plus g2xf3 account for the 3 missing black units. Without spare white units to capture, Black's f-P must have been the unit captured on f3 (i.e. e2-P came from d-file). That leaves Black's missing Q and B to be captured by the a-P, but these captures took place on b6 and c7, both dark squares, and the B is a light-squared one. Hence the third option of c7-c8=Q+ is also impossible.

Therefore the idea of Black playing ...e6-e5+ as the last move leads to an illegal position with the WR giving an impossible check on the 7th rank. If Black's last move was ...e7-e5+, however, the WR wouldn't have been giving check and the position is legal. Thus ...e7-e5+ is proved to be the only possible last move and this enables the e.p. mate-in-1.

Excellent retro composition, Arisktotle!