The Lemon Fool

.  --- --- --- --- --- --- --- ---
8 |   |   |   |   |   |   |   |   |
   --- --- --- --- --- --- --- ---
7 |   | p |   | p |   |   |   |   |
   --- --- --- --- --- --- --- ---
6 |   | N | p | P | p |   |   |   |
   --- --- --- --- --- --- --- ---
5 |   |   | k |   | P |   |   | B |
   --- --- --- --- --- --- --- ---
4 | P |   |   |   | p |   | p | B |
   --- --- --- --- --- --- --- ---
3 | p |   |   | p | P |   |   |   |
   --- --- --- --- --- --- --- ---
2 | P |   |   | P |   |   | K |   |
   --- --- --- --- --- --- --- ---
1 |   | R |   |   |   |   |   |   |
   --- --- --- --- --- --- --- ---
    a   b   c   d   e   f   g   h

It is high time for another chess puzzle. White to move and mate in four moves. Every black move is forced. This may make it seem trivial but “you will do well to crack it in 15 minutes” (says the setter). White is shown here as red [and in capitals].

Cinelli

Good grief, one wonders how it could get into that position with the pawns (on both sides!). Anyway, here's a playable board with it set up:

https://lichess.org/editor/8/1p1p4/1NpPp3/2k1P2B/P3p1pB/p2pP3/P2P2K1/1R6_w_-_-_0_1

cinelli wrote:It is high time for another chess puzzle. White to move and mate in four moves. Every black move is forced. This may make it seem trivial but “you will do well to crack it in 15 minutes” (says the setter). White is shown here as red [and in capitals].

Cinelli

Thanks for the puzzle, does 'forced' mean that each white move must put black into check\checkmate? I think I can see mate in 4 but 1 move does not give check.

RC

ReformedCharacter wrote:

cinelli wrote:It is high time for another chess puzzle. White to move and mate in four moves. Every black move is forced. This may make it seem trivial but “you will do well to crack it in 15 minutes” (says the setter). White is shown here as red [and in capitals].

Cinelli

Thanks for the puzzle, does 'forced' mean that each white move must put black into check\checkmate? I think I can see mate in 4 but 1 move does not give check.

RC

No, it cannot.

You can enumerate checks for the first move, and the only one that forces black's move is to give away the rook. But the near-stalemate leaves black just the one (pawn) move in the position shown, and either sacrificing any white piece to a pawn or moving the king feeds black more forced pawn moves.

I was wondering if it might involve a bishop sacrifice and an en-passant. But that doesn't seem to work, and I'm just heading out now.

ReformedCharacter wrote:

cinelli wrote:It is high time for another chess puzzle. White to move and mate in four moves. Every black move is forced. This may make it seem trivial but “you will do well to crack it in 15 minutes” (says the setter). White is shown here as red [and in capitals].

Thanks for the puzzle, does 'forced' mean that each white move must put black into check\checkmate? I think I can see mate in 4 but 1 move does not give check.

The normal meaning of a move being 'forced' is that there is only one legal move for the player of the move. For example, if it were black's move in the position in the diagram rather than white's, the only move black could make would be to advance the g4 pawn to g3, since all the other black pawns are blocked and all unblocked black king moves would be moves into check, so black's move would be 'forced'.

Gengulphus

ReformedCharacter wrote:does 'forced' mean that each white move must put black into check\checkmate? I think I can see mate in 4 but 1 move does not give check.

'
Although a check is an obvious way of "forcing" (or at least restricting the choices for) your opponent's move, in puzzles that is usually not the case. Puzzles are something of an artform where the "key" to the solution is often a very quiet and unobvious move, perhaps involving a sacrifice to open up a line or close off an escape route for the King. Contrast this with the beginner habit of always checking if you can, which is rather crude and often ineffective. ("Never miss a check, it might be mate" is an old chess joke).

Puzzles are about elegance and efficiency. Note also that good chess players are not always good chess puzzle solvers, and vice versa.

Gengulphus wrote:The normal meaning of a move being 'forced' is that there is only one legal move for the player of the move. For example, if it were black's move in the position in the diagram rather than white's, the only move black could make would be to advance the g4 pawn to g3, since all the other black pawns are blocked and all unblocked black king moves would be moves into check, so black's move would be 'forced'.

Yes, although I think there is another sense of the word "forced" which means that, whilst there is a choice of more than one legal move, only one doesn't lose immediately.

So some puzzles might say "white to play and win in four" but if black plays a move other than the best move, he loses in less than four. So that best move is "forced" if you want to survive as long as possible.

Hint: there is no check until white's fourth move.

Cinelli

I should possibly say that I'm not going to try to answer this one on the board. I do know the answer, and feel that it's quite an elegant chess problem - but unfortunately the way I know it is by having been a bit careless about investigating it with the aid of mc2fool's lichess link...

Gengulphus

mc2fool wrote:Good grief, one wonders how it could get into that position with the pawns (on both sides!).

It is just about possible. The black pawn on d3 could have started out as a f pawn, and made two diagonal captures. The black e pawn started out as the g pawn and made two captures. And the black g pawn started out as a h pawn with one diagonal capture.

Something similar for the white pawns.

It matters because if the puzzle is from an actual game then there could be redundant pieces, i.e. pieces that do not feature in the solution. Whereas if designed as a puzzle (probable) then there is no wasted piece - everything on the board is there for a reason.

If we assume the latter then the key to me is that those two white bishops on the h file have to get into the action. I have not solved this, but one idea is that there is a white king move. This would allow black's 3 moves to be the advance of its g pawn to the first rank. And that then leaves white 3 other moves to work in the bishops. But that said I can't see it, so I might be completely wrong!

I think I had better answer this puzzle, by Fritz Giegold (Die Welt, 1968). The solution is as follows:

1 Be1! g3
2 Be2! dxe2
3 Rb4! Kxb4
4 d4 mate.

Cinelli