[Retros] e.p.##

[Noam Elkies]

UR writes:


> Looking for an en-passant proof game I found nothing shorter than:

> rQ1q1bsr/p1p1pppp/kP1p4/8/R2P4/8/1PPP1PPP/1SB1KBSR  SPG 8.5


Richard Stanley already attained 8.5 in May 1996 on the other side
of the board:

1 c3 f6 2 Qa4 Kf7 3 Qxd7 Kg6 4 Qxe7 Kh6 5 Qf7 Ne7
6 h4 Nc6 7 h5 Na5 8 d3+ g5 9 hg ep##

A few days later Richard reported:


> Matti Mylliemi (Europe Echecs, 1966) has an SPG in 9.5 moves that

> ends with an en passant mate, before which White castled and Black

> promoted a pawn to a bishop.


and writes that this Valladao SPG can be found in Wilts and Frolkin.
In June 1996, Gerd Wilts and Norbert Geissler found the following
in 7.0 moves:

1 f4 e5 2 Kf2 Qh4+ 3 Kf3 Qf2+ 4 Kg4 h5+ 5 Kh3 h4 6 e4 d5+ 7 g4 h:g3 ep##

There's really no reason to limit ourselves to White checkmates,
but even the White-wins version of this is a move shorter
than the 8.5 movers previously seen.  For instance,

1 e4 f5 2 Bb5 Kf7 3 Qh5+ Kf6 4 Qf7+ Kg5 5 h4+ Kh6 6 h5 a6 7 d3+ g5
8 hg ep## (C+, 1.8 msec.)

All of these show the curious double checkmate made with
neither check given by the piece White just moved.
Theodore Hwa observed (30 May 1996) that an ep mate
in a sound SPG must be either a discovered check
or this kind of double check.

NDE