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# Another Selfmate in 1

• #1

Selfmate in 1
• #2
Stigmatisert wrote:

I can't move any white piece!

Correct. It is set up as a diagram, not an interactive puzzle.

• #3

Qb6! forces axb6 and mate

• #4
mapearson1990 wrote:

Qb6! forces axb6 and mate

Almost ... but white has axb6.

• #5

What was black's last move?

Apperantly it could only have been b7-b5. And then you have a solution.

However, after retracting b7-b5 I can see no legal move to retract for white. Even if there was a white knight on a3.

• #6
shoopi wrote:

What was black's last move?

Apperantly it could only have been b7-b5. And then you have a solution.

However, after retracting b7-b5 I can see no legal move to retract for white. Even if there was a white knight on a3.

Good catch. The problem is solveable as given, but I don't want this flaw in it. Let's try this version:

Selfmate in 1
• #7

Surprisingly, the position still seems illegal. The reason is that white's pawns must have made at least 7 captures. A quick count shows that black is missing 7 pieces. But... if the last move was b7-b5 then of coures, the bishop on c8 couldn't have been captured by a pawn.

Very easy to fix though. Just edit the position and remove the a2 pawn (not sure why it's there in the first place as it is not needed, maybe just an oversight).

The solution of course would be:

1. axb6+! en passent (black must have played b7-b5 the move before) 1... Qxc4#.

• #8

No, this is all intentional. If all I wanted was a selfmate by en passant, I would remove many more pieces besides Pa2. To be fair, I should mention that I am violating a certain chess.com convention. But I am conforming to the rules of chess.

• #9

In a selfmate you force your opponent to checkmate you.

• #10

Maybe I'm mistaken, but perhaps the trick is that because black has no legal last move, it must be black to move? And then the solution is 1... Nb7+.

By the way if this is the case, I have found a way to post a position withought elaborating on which side is to move. Simply choose "Game or sequence of moves", and make sure not to put any moves in. That works!

• #11

Qb7, which forces Nxb7#.

• #12

That's not mate, since white can play 2. cxb7+.

• #13
shoopi wrote:

Maybe I'm mistaken, but perhaps the trick is that because black has no legal last move, it must be black to move? And then the solution is 1... Nb7+.

By the way if this is the case, I have found a way to post a position withought elaborating on which side is to move. Simply choose "Game or sequence of moves", and make sure not to put any moves in. That works!

Yes, that's the intended solution. Retro-analysis proves that black has the move, so it has to be 1...Nb7+.

• #14
Test: It works! Thanks for the tip.
Oh, good. You can still use a FEN string. I thought I was going to have to drag all the pieces on the board for a minute there.

• #15

The other benefit, since the FEN is hidden like this, is that castling and en passant rights are also unknown

• #16

hmm well, is the solution a5 e.p. b5 with check bc4, rxc4?

• #17

axb5 en passant?

• #18

GAH necro plus lack of thinking. When you see this sort of ridiculous position with ridiculous conditions, your first thought should be "retrograde puzzle". Solution (shoopi got it first a long time ago) as follows.

If it's black to move, solution is 0...Nb7+ 1. cxb7#. No issues here as white can retract, say wPe4xbNd5.

If it's white to move, black must have moved last ...b7-b5 (since any other black last move gives impossible check situations) and white goes 1. axb6+ e.p. Qxc4#. Now, why is this wrong?

White's pawns must have made at least 7 captures (for instance bxa, cxbxa, exdxc, fxexd.) Now, at first glance black is missing exactly seven men (3P, N, 2B, R) so it seems possible, BUT since black only just played ...b7-b5, black c8-bishop couldn't have escaped and was captured on its home square! So white's pawns could only have taken 6 men and the position is impossible (with white to move.)

Therefore, in the diagram it is black to move, and the solution is after all 0...Nb7+ 1. cxb7#.

• #19
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