[Retros] shortest proofgames of castling switchback

[Noam Elkies]

On Mon, 16 Jul 2007 17:54:20 +0900 (JST),
Hirokaz ONODA <glkoon at yahoo.co.jp> wrote:
 

> Captureless: vacant


Interesting challenge.  I think the following works:

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

  NDE 15.vii.2007

  rQB1k2r/p1pppp1p/np3npR/1b2b3/P6P/1P1PR1Pq/2P1PP1B/1N2K1N1

also, with a very similar invading-Queen mechanism, a bit longer
(even excluding the mating finale) but with a few more features:

  . n . . . . n .  hg-21.5
  . p p . p . . .
  . . . p . p p b
  p . . . . r r p
  . . . Q . . k .
  . P N . . B P b
  P . P P P P . P
  R q B . K . N R  16+16

  NDE 16.vii.2007

  1n4n1/1pp1p3/3p1ppb/p4rrp/3Q2k1/1PN2BPb/P1PPPP1P/RqB1K1NR

I hope these can be tested [and not cooked ;-)] by computer;
the next message gives the intended solutions.

--Noam D. Elkies