[Retros] shortest proofgames of castling switchback

[Hirokaz ONODA]

Hi,

Thank you, Mario and Joost.

So we have this for the shortest PG for castling switchback.
1.e4 f5 2.Bc4 f4 3.Ne2 f3 4.0-0 fxe2 5.f3 e1=R 6.Kf2 Re3 7.Rh1 Rd3 8.Ke1
(Joost de Heer, 2005)

Without promotion:
1.c4 e6 2.Qa4 Ba3 3.c5 Nh6 4.Qh4 0-0 5.Qxd8 f6 6.Qxc8 Kf7 7.Qxb8 Rh8 8.Qxa7
Ke8 (Andrew Buchanan, 2005)  

Captureless: vacant

Q-side castling switchback: vacant
cf.(after O-O-O, K returns, but R does not):
1.d4 c5 2.Bh6 cxd4 3.Qxd4 Nxh6 4.Nd2 Nf5 5.0-0-0 Nxd4 6.Re1 Nxc2 7.Kd1 Nxe1
8.Kxe1 (Christoph Fieberg, 2005)

Castling switchback for both sides: 
r1bnk2r/pp1p2pp/2n2p2/2bQp3/4Pr2/5PR1/PP1P2PP/RNB1K2R
SPG 19.0 14+15 C+
(Andrei Frolkin 2nd Prize Die Schwalbe 1990)

Amici Sumus,
Hiro


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