[Retros] Two little SPG-challenges

[Noam Elkies]

Mario wrote:

M> I would wish the programmers of Natch & Co. would provide a switch,
M> which forces the detection of shorter solutions.
M> Is there any specific reason not to do so?

I replied:

N> If all else fails you can ask Natch to solve the same position
N> in 6.5, 6.0, etc.

Mario:


>  I know. (And hopefully enough all SPGs which are marked 'C+'

> in journals or databases are tested that way :-)).

> For my two toy examples this approach doesn't require much additional

> time. But for longer SPGs (where the solving time might be e.g.

> 3 weeks) it would be nice to know that no shorter solutions exist.


I don't have any first-hand experience with Natch, but I imagine
that for most SPG's in N, once Natch has solved it in N moves
it would still take only a fraction of the time to check
for solutions in N-0.5 or N-1.0, and a tiny fraction
for even shorter solutions.  For all I know, it might not even
save that much time for this search to be done together with
the full-length solution.

N> There are quite a few SPG's satisfying this condition
N> where the K-trek is motivated by parity.  Some years ago
N> I composed one in which the Black King makes 15 of Black's
N> 19 moves and goes back home to be checkmated.  

M> Does that mean you managed to improve/prolong your entry to
M> the 1st Retro List Quick Composition Tourney 1997 on this list?
M> (fen=KnQ1kbnr/1p1ppppp/p1p5/2B5/8/1PP5/P1P1PPPP/RN3BNR,
M> http://www.janko.at/Retros/RML/1997/N00-Tourney.htm),
M> where the ratio was 9 out of 14 black moves made by black king?

No, the SPG I have in mind is even earlier, see for instance
<http://www.math.harvard.edu/~elkies/FS23j.03/spg20.pdf>.
Unlike the 1997 SPG, this one was not constrained by the condition
that the other side also move its King during the K-trek.

NDE