[Retros] Castling in PG's

Noam Elkies elkies at math.harvard.edu
Thu Feb 10 10:34:45 EST 2005

I wrote:

>> Thanks to Francois Labelle for sharing his latest findings!

>> The castling problems are particularly lovely.

Francois replied:

> Thanks. I liked them too, but didn't imagine they were that good.

> I thought that the castling had to be completely invisible for

> a castling problem to be good.

It's true that the castling element is more valuable when
the castling is better hidden, but one must consider this
in the context of the "at-home" constraint (and also
the 7.0 move limit: in Michel's clever 9.0-mover the Qd8
has time to provide additional camouflage). In any case
there is paradox when the King castles and returns
to its initial square in a (S)PG.

All of which raises the question: what's the shortest (S)PG
in whose solution one side castles and then plays both King
*and* Rook back to their initial squares? Is this
within the range of your program? Apologies if you've
already posted the answer and I've forgotten...


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