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MatPlus.Net Forum General Dumb Duals
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(1) Posted by Hauke Reddmann [Sunday, Nov 18, 2018 16:16]

Dumb Duals

Sometimes the following happens:

1...X~ 2.A
1...X->y?? 2.A,B

I.e. duals by Black playing extra dumb. Also works in 2nd degree,
where it is even sillier. (E.g. 301642 YACPDB, yesterday the
author complained bitterly that 1...Sd6 was seen as a dual.
It does not defend against 2.Bxd5. I tend to be sympathetic.)

What is your opinion on the matter? After all, if Black doesn't
defend against the primary threat, noone tends to care...

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(2) Posted by Geoff Foster [Tuesday, Nov 20, 2018 08:20]

Here is the problem referred to by Hauke.

Dieter Berlin, Die Schwalbe 1980
(= 9+12 )

1.Sxa4! (>2.Qd4)
1...S~ 2.Bxd5
1...Sf6 2.Rxc6
1...Sd6 2.Rxc6,Bxd5
1...Sg5 2.Sd2
1...Sc3 2.Sb2
1...Sc5 2.Sb6
1...Be3 2.Sxe3
1...Qg1 2.Be2

I would count 1...Sd6 2.Rxc6,Bxd5 as a dual, because 1...Sd6 is not a silly move. It is just a "random" move that happens to make the same error as 1...Sf6.
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(3) Posted by Hauke Reddmann [Tuesday, Nov 20, 2018 11:00]

But that's the point - you don't consider "random" moves
in the 1st degree.

(= 3+2 )

1.Kc8! (2.Db8) Rb7/Rc7 2.Qxb7/Sxc7

Would anybody claim 1...Ra~ as being dual- or Ra6 as even trialistic?

Thus the author claims you simply don't walk into Mordor or play
a move that doesn't defend against Bxd5.
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(4) Posted by Georgy Evseev [Tuesday, Nov 20, 2018 17:08]

Strictly speaking, any move of Se4 defends against 2.Qd4. So, S~ designation really means "any knight move not shown separately". So yes, it includes Sd6 and masks the dual.
How serious this dual is - is a separate question, with different answer from different judges.
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(5) Posted by Geoff Foster [Tuesday, Nov 20, 2018 22:32]

For black correction the play really needs to be completely accurate, otherwise the logic is spoiled. Here 1...S~ 2.Bxd5 is not strictly true, because one of the random moves is 1...Sd6, for which another mate exists. The point is that 1...S~ 2.Bxd5 appears in the solution, whereas other play such as 1...Qd7 2.Qd4,Be2 does not.

The quality of the play also has to be taken into account. For example, 1...d4 2.Qxd4,Sb6 is unpleasant, because it is a complex white interference mate and repeats the thematic variation 1...Sc5 2.Sb6.
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(6) Posted by Hartmut Laue [Wednesday, Jan 9, 2019 17:33]

If the square e4 is vacated (in any way), the threat 2.Qd4# is parried, but simultaneously the new mating move 2.B:d5# is principally enabled. Relevant for the logic of a black correction are therefore only those moves of the bSe4 which prevent this standard answer (on top of the refutation of the threat which is automatically given by each move of the bSe4) - but not the examination of each move of the knight with respect to further possible mating moves besides 2.B:d5#.

So, logically, 1.- Sd6 is a "silly move" indeed. It is not better than any other move of the knight. The only better defences are 1.- Sc3!, 1.- Sf6!. Why should one look at this move (1.- Sd6) at all when the logic requires to look only at moves which prevent 2.Bxd5#? A black correction asks for stronger moves, not for moves which do not help against the standard answer or (as in this case) make things even worse.

A different point is that of aesthetics. Arbitrariness of moves of some unit is frequently found in presentations of correction play, but it is not compulsory. (There are many renderings where there are exactly two defences, and one of them is a correction of the other.) I do, however, understand a point of view which finds it disturbing if arbitrariness is given (as in Berlin's 2-mover) but with duals after a specific choice of the "arbitrary move". If arbitrariness is seen as the main point, one should clearly expect that each answer is unique. If correction play is seen as the main point, choices of moves which do not correct the primary error of a defence are irrelevant. Still it may aesthetically be felt as a flaw if there exists a choice which allows a dual. Here I agree with Georgy Evseev: "How serious this dual is - is a separate question, with different answer from different judges."
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MatPlus.Net Forum General Dumb Duals