[Retros] At home proof games in 7.0 moves

Joost de Heer ildjarn666 at linuxmail.org
Thu Feb 10 17:21:48 EST 2005

> >> (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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