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MatPlus.Net Forum General To Parry, or Not To Parry?
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(1) Posted by Dan Meinking [Thursday, Feb 25, 2010 19:46]

To Parry, or Not To Parry?

About a month ago, I realized that an original of mine might not be a true "Parry Series":

DM original
(= 5+2 )

phser-s#12 (5+2) C- (or pser-hs#12, if you prefer)

Solution: 1.Rh1+ Sh6 2.Rc8+ Kg7 3.Rg1+ Kf7! 4.Rf1+ Sf5 5.Rc7+ Ke6 6.Sc5+ Kd5 7.Rd1+ Sd4 8.e4+ Kc4 9.Sb7+ Kb3 10.Sa5+ Ka2 11.Rc2+ Ka1 12.Sb3+ Sxb3# S-rundlauf, and wR/wR return to their diagram squares. C+ for last 9 moves.

Originally, I'd hoped to start wK->e1,Rd1->a1 for 1.0-0-0 (13-mover). But... Kostas cooked it in short order with: wKf1/bKf3 for Sb3-d2+ Sxd2#. So, I lopped off the first move and didn't give it a second thought.

Later, it occurred to me that without 1.0-0-0, every move was a check-and-parry. So perhaps this wasn't a Parry 'Series' at all, but rather "hs#12 WhiteUltraSchachZwang" (WUSZ), which is sometimes written as "white must check". Indeed, the diagram tests C+ for the last 9 moves using WUSZ, same as the pser-* form.

To Parry, or Not To Parry? That is the question!

There is some risk to using pser-* vs. WUSZ or BUSZ. A problem that tests C+ for WUSZ or BUSZ may not be C+ for pser-*. But a C+ pser-* (all-checks) will always be C+ as WUSZ/BUSZ because there are fewer legal moves in the latter form.

The best rationale I can give for leaving this as a Parry Series is that it's a better solver problem. Why? Because the solver doesn't know, then, that all moves 'must check'.

I'd be curious to hear other opinions on this.

Incidentally, as I reviewed the recent Good Companions quick-tourney entries, I found a "phser A->B in 37 moves" with all checks by black! Again, one can make the case for pser-* or BUSZ. But in the end I gave it 4th Honorable Mention -- a fine entry by Cornel, as it turned out. :-) You can find it, and the other QCT awards, in the related thread under "Competitions".

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(2) Posted by Cornel Pacurar [Thursday, Feb 25, 2010 20:46]

During the tournament I worked (on my own and together with other composers) on two task ideas:

- the highest number of check-and-parry moves.
- the highest number of consecutive check-and-parry moves.

The special prize has 55 check-and-parry moves, and the 4th HM has 37 consecutive check-and-parry moves. Having only check-and-parry moves was just a bonus, as the problem can easily be extended, in several ways, with a few non-checking moves, thus eliminating the BUSZ dilemma!

On the other hand, yes, indeed, UltraSchachZwang provides a very good and quick way to partially test 'all-check' pser-* problems - thanks for pointing this out last Friday!
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MatPlus.Net Forum General To Parry, or Not To Parry?