[Retros] Twisted knights

[raosorio at fibertel.com.ar]

Hi Nicolas,

We worked this matter during 2006 and published in Problem Paradise a couple
of PGs, not focussed on shortest length record but in the 6 knight moves to get the
sibling and the complementary play strategy.

I reproduce here the sending to Satoshi,

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We made a research on the PDB and found that there are 15 PGs that show
a mutual sibling of knights.  We made the following technical evaluation:

a) The arguments of all of them to justify the siblings are a central pawn capture 
or check protection.
b) In these PGs the knigths move 8-12 times. There are no antecedents in the PDB of
mutual sibling using just 6 moves, wich could be named as the "standard
mechanism" in the sense of WCCC Halkidiki 2004.
c) The homebase position is, in some cases,  reached by the sibling side but
not the oposite one.

The Pgs we are sending here make the sibling in the standard way (6 moves) and the
argument is the oposite side promotion instead of captures or check protection.

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Jorge Lois & Roberto Osorio
Argentina
rsbqkbsr/p1p1p1pp/B4Q2/8/2P1PP2/P1p3K1/P6P/RSB3SR
32 single moves      C+

Solution 
1.Pe2-e4   Pf7-f5   2.Bf1-a6   Pf5-f4   3.Pc2-c4   Pf4-f3   
4.Sb1-c3   Pf3xg2   5.Qd1-f3   Pb7-b5   6.Qf3-f6   Pb5-b4   
7.Pf2-f4   Pb4-b3   8.Sg1-f3   Pg2-g1=B 9.Sc3-e2   Bg1-c5   
10.Se2-g1   Bc5-a3   11.Pb2xa3   Pb3-b2   12.Ke1-f2   Pb2-b1=S 
13.Kf2-g3   Sb1-c3   14.Pd2xc3   Pd7-d5   15.Sf3-d2   Pd5-d4   
16.Sd2-b1   Pd4xc3   

Mutual NN sibling (6 moves) motivated by double Ceriani-Frolkin with promotions on
the knights' home squares. Black side finished officer homebase.

------------------------------------------------------------------------------------------------
Jorge Lois & Roberto Osorio
Argentina
1s1qb1sr/p1p2p1p/p2k1p1p/3p3r/8/2P5/PP2PP1P/RSBQKB1R
39 single moves. 13 + 15       C+

Solution
1.Pd2-d4   Sb8-c6   2.Qd1-d3   Ra8-b8   3.Qd3-a6   Pb7xa6   
4.Sg1-f3   Rb8-b5   5.Sf3-h4   Rb5-h5   6.Sh4-f5   Pd7-d5   
7.Sf5-h6   Pg7xh6   8.Pg2-g4   Bf8-g7   9.Pg4-g5   Bg7-e5   
10.Pg5-g6   Sg8-f6   11.Pg6-g7   Sf6-d7   12.Pg7-g8=S Sd7-b8   
13.Sg8-f6   Pe7xf6   14.Pd4xe5   Sc6-e7   15.Pe5-e6   Se7-g8   
16.Pe6-e7   Ke8-d7   17.Pe7-e8=Q Kd7-d6   18.Qe8-a4   Bc8-d7   
19.Pc2-c3   Bd7-e8   20.Qa4-d1   

Mutual NN sibling (6 moves) with Phenix/Ceriani-Frolkin and Pronkin.
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