[Retros] At Home SPGs, and more

[Göran Wicklund (AL/EAB)]

Here is another three solution proof-game. 

Göran Wicklund, Springaren 73, May, -98

rNbqk1nr/ppp2ppp/8/8/8/8/PPP2PPP/RnBQK1NR
SPG 7.0, 3 solutions

Solutions:
1.e4 e5 2.Ba6 Ba3 3.N*a3 N*a6 4.Nc4 Nc5 5.N*e5 N*e4 6.N*d7 N*d2 7.Nb8 Nb1
1.Nc3 Nc6 2.Nd5 Nd4 3.N*e7 N*e2 4.Ng6 Ng3 5.N*f8 N*f1 6.N*d7 N*d2 7.Nb8 Nb1
1.d4 Nc6 2.d5 Nd4 3.d6 N*e2 4.d*e7 Ng3 5.e*f8N N*f1 6.N*d7 Nd2 7.Nb8 N*b1

If you stop at 6.0 moves, you get a two-solution SPG without any common move.

/Göran 

-----Original Message-----
From: retros-admin at janko.at [mailto:retros-admin at janko.at]On Behalf Of
Joost de Heer
Sent: den 28 januari 2004 10:09
To: retros at janko.at; flab at EECS.Berkeley.EDU
Subject: Re: [Retros] At Home SPGs, and more


Hello Francois,


> I assume that you're talking about using a database of *uniquely

> realizable* positions, using the fact that every sub-proof-game of a

> dual-free proof game must be dual-free.


Actually, this isn't true: A proofgame can have a unique solution, but intermediate positions aren't necessarily unique. The uniqueness comes from preserving castling rights or the need for a double-step as last move to allow an ep-capture.

A further question, which might be answered by your method:

One of the 'open' questions from Mark Kirtley's shorties articles (see http://janko.at/Retros/Shorties/index.htm) is: Is there, besides #5 in the second article, another 3-solution proofgame (so not 3-variations, i.e. three different begin moves)? Perhaps your research can give us an answer to this.

Joost
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