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MatPlus.Net Forum Threemovers Mixed dual avoidance & black correction
 
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(1) Posted by Juraj Lörinc [Friday, Jan 22, 2010 12:12]; edited by Juraj Lörinc [10-01-22]

Mixed dual avoidance & black correction


While black correction is usually considered in the departure form (1...X~, Xab! etc.), also the arrival form is known (1...~ab, Xab! etc.). Indeed, there are many problems of this kind, the most frequent probably various problems with blocks on the same square. They might show dual avoidance (any mate possible after random arrival, with dual avoidance effects after specific piece arrivals), or correction (one specific mate possible after random arrival, usually given by at least one specific defence, then correction with other arrivals). However yesterday I have come across interesting threemover combining (in my view) both concepts:

Alexandr Micholap
HM Sachova Skladba 2003
(= 8+12 )

#3

1.Rf7! th. 2.Rxe5+ Qxe5 3.Qxe5#
1...Rd4 2.Qxf3+
1...Scd4 2.Qe3+
1...Sbd4 2.Qd3+
1...d4 2.Qxc6+

Four defences on d4 unpin wQ and block d4, then are followed by sacrifices. The motivation might be in my view explained as follows:

1...~d4 2.Qd3+ or Qf3+

The following two variations show dual avoidance:

1...Rd4 2.Qxf3+ (but not 2.Qd3+?)
1...Sbd4 2.Qd3+ (but not 2.Qf3+?)

And the other two variations correct by disabling both ~ attacks, but enable one attack each)

1...Scd4! 2.Qe3+ (guards both d3 and f3, but unguards e3)
1...d4! 2.Qxc6+ (unblocks d5, but opens c6-e4)

What is your opinion about this structure? Do you know of any other good mixed examples?
 
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(2) Posted by Thomas Maeder [Saturday, Jan 23, 2010 13:09]

 QUOTE 
What is your opinion about this structure?


Interesting.


 QUOTE 
Do you know of any other good mixed examples?


I'm not convinced that "mixed" is the right term.

Reciprocal dual avoidance, as shown by the variations 1.-Rd4 and 1.-Sbd4, means that each of the two variations is a correction of the other. So all four variations of Micholap's problem show Black correction.
 
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MatPlus.Net Forum Threemovers Mixed dual avoidance & black correction