[Retros] Fastest selfmates in 1?

[Elkies, Noam]

F. Labelle <flab at wismuth.com> writes:

> The results are in.
>
> My computer found 60 positions after 5.5 moves where mate is forced next.
> [ . . . ]

Thanks! Glad to see that my pessimism was unjustified:
not only are their four new families but there are new features --
two kinds of discovered cross-check (one of which again allows
Black a spare move), castling, and even a unique sound SPG!

> I manually reordered the computer output to group similar positions
> together. It's possible that the grouping I made is imperfect, so please
> someone review it.

I agree with the grouping, though I suppose some might split the
Kalajdzievski group in two if the Ne4 variant feels more distant than
the fianchetto variants of the two Blijlevens setups.

> Below are the 60 positions in forsyth notation, and after the colon is
> the number of games leading to that position in 5.5 moves. [ . . . ]

> [ . . . ]
> # Noam Elkies
> 1rbqkbnr/p1Nppppp/8/8/8/1nKP4/PPP1PPPP/R1BQ1BNR : 396
> 1rbqkbnr/p1Nppppp/8/8/8/2KP1n2/PPP1PPPP/R1BQ1BNR : 264

Yes, this was the pair I discovered; I see that 396 is the largest count
among them (the next-largest is not 264 but two Kalajdzievski variants,
each with 314, where Black uses the extra ply to forgo one pawn's
double move).

> As the next step, maybe someone (Noam?) can go through this list and
> simplify the exposition by choosing a few representative diagrams and
> describing the variations in text? To help with that, I'm attaching a
> file containing the same list in ASCII diagrams. Make sure to view it in
> a fixed font like Courier.

Thank you for that formatting.  Yes, I should be able to do that before long.

And then what?  Publish the unique sound SPG (are Mark Kirtley's
"Shorties" still a thing)?  Tell Tim Krabbe about it?  Post another answer to
my Chess Stack Exchange question, or leave it to me to report it?

> Attentive people will notice that there is exactly one unique proof game
> in the list (a diagram with only 1 solution): [ . . . ]
> This is an improvement over the PG in 6.0 by James and Noam.

Yes I noticed! :-)

NDE