[Retros] At home proof games in 7.0 moves

andrew buchanan andrew at anselan.com
Thu Feb 10 20:18:54 EST 2005

I apologize (above all to Joost) for continuing to debate such a tiny point.
Many words admit multiple meanings. Sometimes the senses are quite close to
one another, as here.

A recent email stated:

'My "7.0 moves or less" search visited 196221 distinct at-home diagrams, and
found 10300 PGs and 9983 SPGs'.

Here is a gentleman (F.Labelle of Berkeley CA) who is using the terms SPG &
PG in a sense which implies uniqueness.

I rest my case.


PS: I reckon in composition competitions, Francois' program should be given
a two half-move handicap versus humanity!

PPS: What is the 7.0 "at home" composition with castling, and both R & K on
the board?

-----Original Message-----
From: retros-bounces at janko.at [mailto:retros-bounces at janko.at] On Behalf Of
Joost de Heer
Sent: 10 February 2005 22:22
To: The Retrograde Analysis Mailing List
Subject: RE: [Retros] At home proof games in 7.0 moves

> >> (c) SPG without specified number of moves. This is just like a PG

> >> except that the solver has to find the number of moves, which is the

> >> minimum possible in which the position can be reached, and is unique.

> >

> > The term 'SPG' has nothing to do with uniqueness.


> That is not my understanding.


> A common use of the term SPG is to refer to a kind of composition. One

> property of a (sound) composition is that the solution must be unique. SPG

> inherits this property.

I beg to differ. An 'SPG' means that there is no shorter way to reach the
position. Point. There's no reason why this should be unique (remember,
there are enough SPG's with multiple solutions). Equally, a '#2' means that
white plays a move, and mates black after every possible defense. No
uniqueness for either the key move, or the continuation needed. Of course
the value of a composition is not very high if it has multiple solutions,
and they're not connected in a way.

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