Sunday, January 25, 2015

Valladao theme in Proca Retractor

The Valladao task (thus named after Joaquim Valladão Monteiro) is a mix of the three special moves: castling, en passant capture and [minor] promotion, in a single chess problem. Naturally, this blend has attracted many chess composers and the retro genre makes no exception.

In the selected four Proca Retractor compositions the thematic moves appear in the retro play. Interested readers may find other examples in which the castling or the promotion appear in the forward play. (To find them, go to PDB website and search "k='valladao' and stip='proca'")
As usual in Proca Retractors, the main challenge is to ensure there are no duals in the retro or forward play.

The below 1st Prize winner would demonstrate many specific points:

Wenda, Klaus
König & Turm, 2003 (U252)
1st Prize

-11 & #1AntiCirce Calvet
Proca Retractor
No Forward Defense
5 + 6

Show Solution

Walter, Martin
Die Schwalbe, 2006 (13185)

-6 & #1AntiCirce
Proca Retractor
6 + 7

Show Solution

More difficult is to show the retraction of the white castling. The only convincing example so far has been realized by the regretted German expert Wolfgang Dittmann and it is also the first one to show the s#1 stipulation in the forward play.

Dittmann, Wolfgang
Die Schwalbe, Aug 2002 (11589)
2nd Comm.

-4 & s#1AntiCirce
Proca Retractor
6 + 9

Show Solution

The above examples showed Valladao using AntiCirce. It is also possible to mix Proca Retractor with other fairy conditions, as in the next example.

Crişan, Vlaicu
Die Schwalbe, Apr 2013 (260/15553)

-7 & s#1CirceAssassin
Proca Retractor
11 + 5

Show Solution


Proca Retractor definition:
A Proca Retractor is a defensive Retractor. Black is defending by trying to retract the moves that will forbid (or delay) the achievement of White's goal. You may see at the Retro Corner an example by W. Dittmann of orthodox Proca Retractor showing two en passant captures.

Anticirce: the capturing piece disappears and is immediately reborn on its home square while the captured piece is removed for good. The capture is not legal if the rebirth square is not free. A pawn capturing on the eighth rank is first promoted and then reborn on the home square of the promoted man. Here "checks are fairy" i.e. a King is not in check if its "capture" is not legal because the rebirth is not possible.
In AntiCirce Cheylan a piece is not allowed to capture on its home square; in AntiCirce Calvet this is allowed.

Circe Assassin: the captured unit is reborn on its rebirth square even if the rebirth square is occupied. And then the occupying unit disappears for good. Hence a unit on its home square cannot be removed.