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MatPlus.Net Forum General Illegal Clusters
 
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(1) Posted by Geoff Foster [Wednesday, Jul 15, 2009 06:58]

Illegal Clusters


An illegal cluster is an illegal position which becomes legal on removal of any unit (not a King).

T R Dawson, The Problemist Fairy Chess Supplement, 1933
(= 1+2 )
Add black rook and black bishop for an illegal cluster

In the above example the solution is to add the black rook on g4 and the black bishop on h8, which gives an illegal triple check. If any of the 3 checking pieces is removed then the position is a legal double check.

Was Dawson the inventor of illegal clusters? Was the above problem the first one?
 
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(2) Posted by Joost de Heer [Wednesday, Jul 15, 2009 12:25]

According to http://www.janko.at/Retros/Glossary/IllegalCluster.htm: Yes, Dawson invented the genre in 1933.
 
 
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(3) Posted by Kevin Begley [Wednesday, Jul 15, 2009 20:23]

I am not sure you can call this specific problem the "first" illegal cluster.
Dawson published several ICs in The Problemist Fairy Chess Supplement, in 1933.
 
   
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(4) Posted by Joost de Heer [Thursday, Aug 13, 2009 12:03]

From 'Der Blick zurück' (page 53):

 QUOTE 
Eine weitere produktive Erfindung von Dawson aus dieser Zeit ist das Illegal Cluster. 1933 kam er auf die Idee, dass es nicht nur reizvoll, sondern auch ästhetisch ansprechend ("pretty miniatures") sein könne, die Konstruktion einer illegalen Stellung zu verlangen (durch Einfügung bestimmter Steine in ein unvollständiges Diagramm), die durch Entfernung eines jeden Steins (außer den Königen natürlich) legal wird [33]

[33]Dawson, Thomas Rayner: Illegal Positions. In: The Problemist, Fairy Chess Supplement, Februar 1933, Nr. 16, S. 104f.


Which translates to something like:
Another productive find by Dawson from this age is the Illegal Cluster. In 1933 he got the idea that it couldn't be just interesting, but also esthetically pleasing ("pretty miniatures") to demand the construction of an illegal position (by adding certain pieces in an incomplete diagram), which would become legal by removing any piece (except the kings of course).

[33]Dawson, Thomas Rayner: Illegal Positions. In: The Problemist, Fairy Chess Supplement, february 1933, Nr. 16, P. 104-

If you can understand German, this book is a wonderful introduction to retrochess. If you can't read German, it's still a wonderful book with lots of good retro compositions.

The example given in the book is:

T.R. Dawson
The Problemist Fairy Chess Supplement 1933
(= 1+1 )

add (a) , (b) for an illegal cluster
 
   
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(5) Posted by Vladimir Tyapkin [Thursday, Aug 13, 2009 18:11]

Would another twin be possible with adding 4 black pawns on c5, d5, d4, e5?
 
   
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(6) Posted by Dmitri Turevski [Thursday, Aug 13, 2009 18:29]

4-pawns twin has too many solutions (eg a5, a6, b6, b7)
 
 
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MatPlus.Net Forum General Illegal Clusters