# [Retros] Retro-strategy and new AP-type

Valery Liskovets liskov at im.bas-net.by
Tue Jun 26 07:30:00 EDT 2007

Dear Guus,

The intention of your problem is fresh, beautiful and, I believe, correct
in the framework of the AP-logic: indeed, we see a posteriori why B
couldn't (or had the right not to) mate on the 2nd move. A noticeable
(although reflexmate restricted) contribution into the retro-strategy.

However, I have doubts as to the soundness of the problem as is:
in order to postpone castling, instead of immediate 4... Bxg7, Black
could play first 4... Rd8+!, and only after 5.Kc7(xb7) Rd7+ 6.Kc8
take 6... Bxg7, etc. If I'm right, maybe merely the repetition rule

Btw, the additional thematic nuance mentioned by you which is
concerned with the forced illegal reflexmate Ke7# (instead of
compulsory 0-0) would have been very interesting, particularly
if it could arise on greater than n move (in r#n) as the only way
to disqualify some B's attempt.

Valery L.

"Rol, Guus" wrote:

> Dear retro-friends,The solution to the reflexmate problem I posted last

> week is not difficult once you get the right AP (a posteriori) idea. Look

> at the equivalence with e.p in a formal logical context:A Posteriori:1.

> If "castling right" proves "e.p. right" in all proof games then "playing

> e.p". can be justified a posteriori by "castling"2. If "the right to 0-0"

> proves "no right to 0-0-0" in all proof games then "denying the right to

> play 0-0-0" can be justified a posteriori by "0-0" "Denying the right to

> play 0-0-0" in a reflexmate problem is demonstrated by refusing to mate

> through long castling and needs a posteriori justification as shown in

> this composition:Problem:White: Kd6, Bg7, Sd7, P:b6,c4,f5,g6Black: Ke8,

> Ra8, Rh8, Bd8, P:b7,c6,f6,f7.R#6 (AP = A Posteriori).Solution:Note that

> one of the black castlings is illegal.1. Sxf6+ Bxf62. c5 Rd8+! (black

> refuses to 0-0-0 and must justify that by playing 0-0 later)3. Kc7 Rd7+4.

> Kc8 (Kb8? Be5+! Kc8 wastes a move) Bxg7Now white is in zugzwang; black on

> move would be forced to play Ke7 illegal mate!5. Pg6xf7+ Rxf76. Pf6 0-0

> reflexmate!Black is happy to accomplish his 0-0 justification and white

> to get his timely reflexmate. Note that black cannot successfully delay

> the mate with additional checks!Guus Rol.

>

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