[Retros] Shortest checkmates in shortest proof games

[Noam Elkies]

Interesting task; it rings a bell but I cannot recall an exact
anticipation.  Two improvements:


> 9) White checkmates with Rook a1: SPG in 5,5 moves


4.5 moves: 1 a4 b5 2 ab c5 3 R:a7 Qb6 4 Rc7 Qd6 5 R:c8#
(similar to your Rh1 SPG; C+ Popeye 3.41 in 0.04 second)


> 15) White checkmates with Knight g1: SPG in 5,5 moves


4.5 moves: 1 Nf3 g5 2 Ne5 g4 3 N:d7 e5 4 a3 Ne7 5 Nf6#
(C+ Popeye 3.41 in 0.04 second)

Perhaps some more improvements:


> 3) White checkmates with Pawn c2: SPG in 5,5 moves


Again only 4.5 -- if  1 c4 e6 2 c5 Bd6 3 c:d6 Kf8 4 dc d6 5 c:d8=Q#
(C+ Popeye 3.41 in 0.02 second) is allowed...  Likewise the 5.5 moves
for a2,c2,h2 can be reduced to 4.5 with a promotion mate:

1 a4 c6 2 a5 Qc7 3 a6 Qf4 4 ab d6 5 b:c8=Q# (C+ in 0.01 sec.)
1 f4 e5 2 fe Bd6 3 e:d6 Kf8 4 dc d6 5 c:d8=Q# (C+ in 0.02 sec.)
1 h4 c6 2 h5 Qc7 3 h6 Kd8 4 hg h6 5 g:f8=Q# (C+ in 0.02 sec.)

--Noam D. Elkies