Weird Position Challenge

I don't see any response by the checked side with any of the following.

White bishop at c6 or d5
Black bishop at d5 or e4

Originally posted by geepamoogle
I don't see any response by the checked side with any of the following.

White bishop at c6 or d5
Black bishop at d5 or e4

The black bishops can also mate on g2 and h1. The issue is you have to figure out which placement is legal. The bigger issue is that there's only one answer.

Originally posted by geepamoogle
I don't see any response by the checked side with any of the following.

White bishop at c6 or d5
Black bishop at d5 or e4

The colour of bishop to be placed is very straightforward. Not sure as to the square though.

Black bishop at d5, as that's the only spot where the bishop could have moved from a non-checking diagonal.

Originally I hadn't known legality of the position was the essence..

Originally posted by geepamoogle
Black bishop at d5, as that's the only spot where the bishop could have moved from a non-checking diagonal.

Originally I hadn't known legality of the position was the essence..

Why does it need to move from a non-checking diagonal?

Originally posted by SwissGambit
Why does it need to move from a non-checking diagonal?

White player cannot be in check if it is black's move.. And since neither side is in check, that means the added bishop has to have moved from a location where it does not attack the king's square.

Now what I would have to consider is if the final move might have been a promotion, in which case the bishop may have been a pawn before the move, and hence did not check the king..

Comments?

Originally posted by geepamoogle
White player cannot be in check if it is black's move.. And since neither side is in check, that means the added bishop has to have moved from a location where it does not attack the king's square.

Now what I would have to consider is if the final move might have been a promotion, in which case the bishop may have been a pawn before the move, and hence did not check the king..

Comments?

Is it true that the "location where it does not attack the king's square" is always off the diagonal with the B and K?

Your 2nd point is important. What about the possibility of +bBh1, with the last move ...g2xh1=B+?

Here is the full solution to the Bishop problem. Jirakon was the only one who came close to solving it. All he had left to do is prove that there are no 'spare' captures.

Only B@d5 is a legal mate. B@e4 means that Black captured last move (how else to nullify the check?)

8 captures are needed to promote 16 Bishops:


If all the pawns on the 5th rank capture something, they can all promote.

The problem is that we always get an even number of dark- and light-square Bishops. White needs to promote exactly 7 light square Bishops, and Black needs exactly 5. Thus, the last two available captures must be used to change the square color of a wB and bB.

Originally posted by SwissGambit
Here is the full solution to the Bishop problem. Jirakon was the only one who came close to solving it. All he had left to do is prove that there are no 'spare' captures.

Only B@d5 is a legal mate. B@e4 means that Black captured last move (how else to nullify the check?)

8 captures are needed to promote 16 Bishops:

[fen]rnbqkbnr/1p1p1p1p/8/pPpPp ...[text shortened]... Thus, the last two available captures must be used to change the square color of a wB and bB.

This puzzle was way over my head. That was a good one SwissGambit 🙂

legal and it mate in 1... But with shortest proof game, who to?

I see no way of determining whose move it is. Is that what you mean by proving who can be mated? It looks like either white Qf5# or black Qf4# work.

Originally posted by Jirakon
I see no way of determining whose move it is. Is that what you mean by proving who can be mated? It looks like either white Qf5# or black Qf4# work.

"Shortest proof game" means that you have to find the shortest legal game that reaches the position.

Oh. Well in that case, wouldn't everything have to be symmetrical? That makes it White's move, so Qf5#.

Originally posted by Jirakon
Oh. Well in that case, wouldn't everything have to be symmetrical? That makes it White's move, so Qf5#.

Actually, it's Black's move.

Ignoring checks and collisions with enemy pieces, the fastest path to the setup for each side is:

R: 6 moves
N: 6 moves (Nc3-e4-g3 and vice versa)
K: 4 moves (castling makes no difference)
Q: 3 moves (Qh1-e4(d5)-d3
B: 5 moves (one extra move by wBf1 to allow wK/Q to use the long diagonal)
P: 2 moves
----
26 moves

But there's no PG in 26.0. There are too many problems with Q or N checks to the enemy King, and too many Bishop collisions on the long diagonal. It is necessary to make one extra move for White just to avoid checks.

1.b4 g5 2.Nc3 Bg7 3.Rb1 Kf8 4.Rb3 b5 5.Ra3 Nc6 6.Nf3 Rb8 7.Nd4 Rb6 8.Nb3 Bd4 9.g4 Kg7 10.Bg2 Ne5 11.Bc6 Kf6 12.Ne4+ Ke6 13.Kf1 Nf6 14.Rg1 Rg8 15.Rg3 Rg6 16.Rh3 Rh6 17.Kg2 Ng6 18.Kg3 [here's the extra move - it allows the wQ to get in place w/o checking] 18...Nd5 19.Qh1 Ra6 20.Qf3 Nb6 21.Qd3 Qh8 22.Kf3 Qe5 23.Ng3 Qd6 24.Bb2 Bf6 25.Ke3 Bb7 26.Bf3 Bc6 27.Bc3

27...Qf4#

Oh. Okay.