[Retros] Petrovic #8 is C+

[Noam Elkies]

Valery Liskovets <liskov at im.bas-net.by> wrote:


> Concerning the notions of "essential progress" and "position" (and its

> repetition) let me recall the famous chess problem of N.Petrovic

> (The Problemist, 1959, 1 Pr.; P1012540):

>  [r3k2r/p2p4/p1pP2p1/5pN1/5p2/1Q3p2/PP4b1/KB6] #8

> 1.Qb7! Rd8 2.Qb3 Ra8(2) 3.Bd3 Rh1+ 4.Bb1 Rh8(3!) 5.Qc3! Rh7 6.Qf6.


Thank you for this -- as it happens I had been looking for that problem
only a few days before but could not locate it.

I'm happy to report that this classic is C+.  It took Popeye 3.41
more than 4 hours to verify it!  With the "Variation" option,
it produces 700+ moves; to be sure, some are repetitive(*) but there
are still quite a few nontrivial side-lines to check, and the
4-hour timing is some measure of the difficulties Petrovic must
have faced in constructing and checking this problem.

(*) For isntance, it takes 32 lines to give the mate in 2 after 1...0-0?
2 Qxd7.  Even so, some lines are omitted, such as 3...Kd8, which defeats
the threat 4 Qf7+ but allows the short mate 4 Nf7+ Ke8 (Kc8? 5 Bxa6#)
5 Nxh8 and mate next (I also checked with Popeye that there is no other
way for White to mate in time after 3...Kd8).

NDE