Shortest-proof-game challenge
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BishopTakesH7 wrote:
#3593
Mar 7, 2023
0
#3586
There are several games with 20 moves. Would like to lower it to 19 by not “wasting” a move on the h4 capture, but I don’t see how. One idea is to let the e-Pawn take it and promote to N on h1, but I don’t find enough moves for Black in the opening.
EvinSung wrote:
from post 3772 in illegal position contest
Here is a proof game:
lubaza wrote:
There are several games with 20 moves. Would like to lower it to 19 by not “wasting” a move on the h4 capture, but I don’t see how.
For PG in 19.0, Natch finishes with 0 solutions after analyzing 48195 positions.
Mar 7, 2023
0
#3589
Are there any proof game finders that work on Mac? Because I can't find any.
BishopTakesH7 wrote:
Are there any proof game finders that work on Mac? Because I can't find any.
Natch and Euclide both run from a DOS command prompt. Maybe you could run them from a DOS emulator on your Mac.
n9531l1 wrote:
BishopTakesH7 wrote:
Are there any proof game finders that work on Mac? Because I can't find any.
Natch and Euclide both run from a DOS command prompt. Maybe you could run them from a DOS emulator on your Mac.
I just noticed that you can set up Euclide in Mac OS X. Instructions are in the document at
http://lestourtereaux.free.fr/euclide/euclide.html
The instructions include the comment, "Note that the above steps have been tested on Mac OS X 10.6, known as Snow Leopard. The above steps are probably difficult for a casual Mac user but they nevertheless allow Euclide to be run for those that can follow them."
lubaza wrote:
#3597
There are several games with 20 moves.
Here's one of the other ways, with Black promoting a different pawn and not castling.
Mar 8, 2023
0
#3593
n9531l1 wrote:
lubaza wrote:
There are several games with 20 moves. Would like to lower it to 19 by not “wasting” a move on the h4 capture, but I don’t see how.
For PG in 19.0, Natch finishes with 0 solutions after analyzing 48195 positions.
I can show 19 is impossible. Least number of Black moves is 7 for Pawns (dxc6, hxg6, 5 moves to necessary N promotion), 4 for Knights (b8-d7-b6 and d1/h1-f2-d3 only possibility), 2 for Bishop and 1 for Queen = 14 + K/R moves. The King needs a move, so maximum 4 moves to get the Rooks to their positions. That rules out another promotion or moving Ra8 to g1. So the only possibility for K/R moves in a 19.0 PG is Rh8-h1-g1 and either Ke8-d8-c8 + Ra8-a4 or 0-0-0 + Rd8-d4-a4. White must capture one of the Pawns on a7/e7, the other one promotes.
So how does Ph2 disappear? It never captures anything since the only capture by White is on a7 or e7, so it must be captured in the h-file before Rh8-h1. Qd8-h4 happens after Rh8-h1 so only possibility to capture the h-Pawn is by the Black e-Pawn before it promotes on h1.
Blacks first move must be e7-e5, from there the Pawn must go e5xf4xg3xh2-h1N. White can not get a piece to c6 or g6 in two moves, so he must get something to f4 in two moves to not delay Black's progress. So within the first three moves, White must get a piece to f4 and another piece to g3, c6 or g6 to not delay Black, which is impossible in this game. Therefore no 19.0 PG exists.
A pity, because if we cheat by playing an early double-move on each side, there is a 19.0 "game" with some interesting details. As my game example went, Black must castle since a White N must be captured on a dark square due to parity of Ra1-b1 moves, and d4 is the only dark square available in time. The cheating game goes 1. c2-c4 e7-e5 2+3. c4-c5-c6 d7xc6 Nb8-d7 4. f2-f4 e5xf4 which saves one move from this example.
Mar 8, 2023
0
#3594
Here is the example that brought me to this thread. It's a slight modification of a retro chess puzzle you might know and which I really liked. I am pretty sure I have found the length of the SPG games, but I leave it to you first.
lubaza wrote:
Here is the example that brought me to this thread. It's a slight modification of a retro chess puzzle you might know and which I really liked. I am pretty sure I have found the length of the SPG games, but I leave it to you first.
That position reminds me of one I posted before in another thread (posts #6521 and #6522 there), although it is reflected and the black rook does not give check. It has to do something with the 75-move rule, although I have yet to make a proof game of it.
Mar 8, 2023
0
#3596
daStrwbrry wrote:
lubaza wrote:
Here is the example that brought me to this thread. It's a slight modification of a retro chess puzzle you might know and which I really liked. I am pretty sure I have found the length of the SPG games, but I leave it to you first.
That position reminds me of one I posted before in another thread (posts #6521 and #6522 there), although it is reflected and the black rook does not give check. It has to do something with the 75-move rule, although I have yet to make a proof game of it.
That is correct! I reflected it just to create an extra move in the SPG, and I put the R on d8 to make an extra half move. It can only be retracted to d7 to have a legal position.
And yes, the 75 last moves on both sides (76 for Black with my extra move) are neither captures nor Pawn moves. So either player could claim a draw after 50 such moves, the tournament arbiter after 75, but the claims must be made, otherwise the game goes on.
lubaza wrote:
That is correct! I reflected it just to create an extra move in the SPG, and I put the R on d8 to make an extra half move. It can only be retracted to d7 to have a legal position.
And yes, the 75 last moves on both sides (76 for Black with my extra move) are neither captures nor Pawn moves. So either player could claim a draw after 50 such moves, the tournament arbiter after 75, but the claims must be made, otherwise the game goes on.
It is indeed a very clever retro puzzle as the rooks have to go back and forth, just for the black rook to get around the white king.
Anyway, here is an optimal proof game. Getting the black king to g3 in 5 moves without trapping any white units was the hard part, but nonetheless possible:
Mar 8, 2023
0
#3598
daStrwbrry wrote:
lubaza wrote:
That is correct! I reflected it just to create an extra move in the SPG, and I put the R on d8 to make an extra half move. It can only be retracted to d7 to have a legal position.
And yes, the 75 last moves on both sides (76 for Black with my extra move) are neither captures nor Pawn moves. So either player could claim a draw after 50 such moves, the tournament arbiter after 75, but the claims must be made, otherwise the game goes on.
It is indeed a very clever retro puzzle as the rooks have to go back and forth, just for the black rook to get around the white king.
Anyway, here is an optimal proof game. Getting the black king to g3 in 5 moves without trapping any white units was the hard part, but nonetheless possible:
Very well, and most of it in line with my solution. But it is not the shortest possible.
lubaza wrote:
daStrwbrry wrote:
Anyway, here is an optimal proof game. Getting the black king to g3 in 5 moves without trapping any white units was the hard part, but nonetheless possible:
Very well, and most of it in line with my solution. But it is not the shortest possible.
I would have been proud if I had found a proof game of any length.
In Die Schwalbe I just found an entry for a 185-move non-unique SPG.
Thanks for your reply. That is really impressive! By searching, I found this one from 2018, probably the same source?
The reason why I asked was because I knew about another retro puzzle that needed a lot of moves to release the position and tried to find a SPG for it (with some minor adjustments). Far less than 185, bit still big though. Will post the challenge here, and I'm pretty sure I have found a SPG.
They are the one and the same 185.