[Retros] shortest proofgames of castling switchback

[Noam Elkies]

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


> [NDE wrote:]



> | 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

> | 

> | ... Does this work?



> Maybe you should put the black rook Rf8 on e8 instead,

> otherwise the following cook is possible: [...]


Indeed I had neglected to check Black's 0-0 options...
Yes, please change 19...Rf8 to 19...Re8, thanks.

Meanwhile I have a potential fix for the 19-move attempt at a
White castling switchback in a captureless sound helpgame:
change the sequence 12 Re3 Qf3  13 Bh2 Qh3  14 g3  to
12 Rg3 Qf3  13 Rg5 Qh5  14 g4,  giving this diagram:

  r Q B . k . . r  hg-19.0
  p . p p p p . p
  n p . . . n p R
  . b . . b . R q
  P . . . . B P P
  . P . P . . . .
  . . P . P P . .
  . N . . K . N .  16+16

  NDE 17.vii.2007

--Noam D. Elkies