# PG in 20.0 moves [2/26]

SwissGambit
Posers and Puzzles 26 Feb '08 19:48
1. SwissGambit
Caninus Interruptus
26 Feb '08 19:48

Proof Game in 20.0 moves
[Find a legal game that reaches this position after Black's 20th move]

Please PM any solutions so that others have a chance to solve it.

Composer's name will be given later.
2. 26 Feb '08 22:31
SwissGambit, are you interested in other types of chess problems, or only/mainly in PGs?
Do you compose PGs yourself?
3. SwissGambit
Caninus Interruptus
26 Feb '08 22:381 edit
Originally posted by David113
SwissGambit, are you interested in other types of chess problems, or only/mainly in PGs?
Do you compose PGs yourself?
I like retrograde analysis, helpmates, and series problems also.

Yes, I've composed some PGs.
4. 29 Feb '08 00:21
Got it!
5. SwissGambit
Caninus Interruptus
29 Feb '08 00:42
Originally posted by Jirakon
Got it!
Almost...one minor hiccup that should be easy enough to fix.
6. 29 Feb '08 02:25
FIX'D
7. 29 Feb '08 12:12
How do you go about solving proof games?Set up a board and play through? In this example I can see certain moves that need to be made but I wouldn't know what order to put them in or how certain positions would be arrived at.

For instance the white queen, I'm guessing he took the rook on h8 but then why go to g7?
8. 29 Feb '08 13:26
Originally posted by andomasahashi
How do you go about solving proof games?Set up a board and play through? In this example I can see certain moves that need to be made but I wouldn't know what order to put them in or how certain positions would be arrived at.

For instance the white queen, I'm guessing he took the rook on h8 but then why go to g7?
Hmm, the black rook may have been captured on e3 by the white pawn (how else does the pawn get there?), and the knight could have moved out of the way to let the rook out and then back in again. Most moves in a proof game will be non-sensical to a normal chess player--don't think why, but think how?
9. 29 Feb '08 13:37
how does the black pawn get to d6?
10. 29 Feb '08 15:21
Originally posted by andomasahashi
How do you go about solving proof games?Set up a board and play through? In this example I can see certain moves that need to be made but I wouldn't know what order to put them in or how certain positions would be arrived at.

For instance the white queen, I'm guessing he took the rook on h8 but then why go to g7?
My first advice - count the pieces of both sides that are left, account for the possible pawn captures (as here it is obvious that d2xe3 and b7xc6 and e7xd6 were such). You now should have pretty good idea what pieces were captured on that squares (though how they came there is sometimes harder to guess).
What usually helps me tremendously - find the minimum number of moves for White to reach the position (ignore Black). Do the same with Black. Assume shortest paths for all pieces. Most probably one of the sides will have the exact number of moves required in the PG. So if it is White, Black would have to ensure that White can make all that moves in this shortest time (Black plays to assist White, in other word). Look for "spare" moves - moves that don't obstruct the path a piece should go through. These together with some additional info will quickly nail down the order of the moves (the spare moves are usually the first few before Black can unblock some of the paths).
11. SwissGambit
Caninus Interruptus
29 Feb '08 17:24
Jirakon has solved this.
12. 29 Feb '08 18:42
SOLV'D
13. SwissGambit
Caninus Interruptus
03 Mar '08 18:231 edit
Solution:
1.c4 Na6 2.c5 Rb8 3.c6 bxc6 4.b4 Rb5 5.Ba3 Re5 6.b5 Re3 7.dxe3 Nh6 8.Qd6 exd6 9.b6 Qg5 10.b7 Be7 11.b8=Q O-O 12.Qb2 Bb7 13.Kd2 Ra8 14.Kc3 Nb8 15.Kb4 Kf8 16.Qxg7+ Ke8 17.Nc3 Bf8 18.Rb1 Qd8 19.Ka5 Bc8 20.Rb7 Ng8

It seems paradoxical that Black has to clear the entire back row just to play the one move Rh8-a8. The key lies in the two bP captures. White is missing Pb and c, but Black captured on c and d. White would need to shift his pawns one file each to avoid having to promote. The trouble is that one of Black's two missing units is Pg7, which is too far to sac to a wP.

So, White has to promote, and we can follow ilywrin's suggestion of counting the minimum number of moves needed for each White piece.
2 - Rb7
2 - Qg7
4 - Ka5
1 - Ba3
1 - Nc3
1 - Pe3
-----
11 total

Add moves by the 'hidden' pieces:
5 - Pb2 promoted
3 - Pc2 sacrificed itself on c6 [no reason to shift files here]
1 - Qd1-d6 [fastest possible way to sacrifice on d6 - since we're promoting, this is OK. The promoted piece can get to g7 just as fast as the original Q can.]
-----
20 total

White's 20 moves are all spoken for. His schedule of moves gradually forces the conclusion that bR will travel along the 8th rank. Pg7 will be captured late in the game, so the g-file does not work out. The e-file is too crowded; it is difficult to shuffle K and Bf8 around the Rook before the promoted Q crashes into g7.

By elimination, the bR must route thru the 8th rank, which works if the moves are carefully timed.

Composer: Satoshi Hashimoto