[Retros] shortest proofgames of castling switchback

[Noam Elkies]

"Mario Richter" <mri_two at t-online.de> writes:


> Dear Noam,



> unfortunately both problems are cooked: [...]


Thanks for this quick check.  At least both cooks exploit
what I knew were weak links in the two sequences (the Re3/Bh2 passage
in the Black 0-0 problem, and the timing of ...h5 in the White one).
I see that the cook of the second problem does not move the Ng1
at all, so it might survive up to 20 0-0, but maybe the following
(without ...h5) works even better:

in 20.5 (switchback is completed after 19.5):
  1 g3 a5  2 Bg2 Ra6  3 Be4 Rf6  4 Nf3 d6  5 0-0 Qd7  6 Kh1 Qh3
  7 Rg1 Qf1  8 b3 Bh3  9 Ba3 Rf5  10 Qc1 f6  11 Qb2 Kf7  12 Qd4 Kg6
  13 Nc3 Qb1  14 Bc1 Kh5  15 Rg2 g6  16 Kg1 Bh6  17 Kf1 Bg5  18 Ke1 Nh6
  19 Rg1 Rf8  20 Rh1 Ng8  21 Ng1

  . n . . . r n .  hg-20.5
  . p p . p . . p
  . . . p . p p .
  p . . . . r b k
  . . . Q B . . .
  . P N . . . P b
  P . P P P P . P
  R q B . K . N R  16+16

  NDE 17.vii.2007

No mate, but at least we have the Bc1 and Ng1 switchbacks, and Black
has a (much more transparent) switchback of his own (...Ng8).
Does this work?

--Noam D. Elkies