[Retros] Accidental retro

[Theodore Hwa]

On Mon, 13 Feb 2006 Pastmaker at aol.com wrote:


>

> Given a diagram position in which there is only one possible last move, is

> there now a program capable of determining that move for all such diagrams?

> (That was not the case some months ago if I recall correctly.)


I don't think there is (anyone, please feel free to correct me if you know 
differently.)  This would seem to be a quite difficult problem, in 
general.  But let me throw out some ideas here.

In a typical 'hard' retro problem, a set of pieces is locked within a set 
of squares S, meaning that no piece currently in S can leave S unless some 
outside piece moves into S.  The key to unlocking the position is figuring 
out the external manuever.  The article 
http://www.janko.at/Retros/Articles/Volet.htm is a good example of this. 
Here S would be the rectangle with opposite corners c8 and h6, plus the 
squares b7, f5, g5, h5.

A general solver, that solves in a reasonable time, would likely need to 
have some kind of module that identifies such locked subsets, and then 
looks for these external moves.  I think this would be the next big step 
in automated retro solving.  Someday I do hope to implement this...

Ted