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:
1.g5xh6 ep.(+wPh2) h7-h5 2.Bg8xRa2(+wBf1) Ra1-a2+ 3.d5xc6 ep.(+wPc2) c7-c5 4.Kc2-b2 Kc8-d8+ 5.Kd1-c2 Ra2-a1+ 6.Ke1-d1 Rd8-e8+
7.Kc1xpb2(+wKe1) b3-b2+ 8.Kd2-c1 Ra1-a2+ 9.Ke1-d2 Ra2-a1+ 10.Ke6xRe5(+wKe1) 0-0-0+ 11.g7-g8=B & 1.Bd5#
The order of moves is very precise. White can’t play directly 1.Bg8xRa2(+wBf1)? because Black can play 1...Qh8-h4+! hence the en passant key, obstructing the black Queen. The second en passant capture is required to free square c2 for the white King and constrain the black Rook e5 on the same file. Black castling is forced as a result of bRe5 checking wKe6.
There is no promotion dual in the forward play, as 1.g8=R? is thwarted by 1...Qh1!
White can’t proceed earlier with the main plan 7.Ke6xRe5(+wKe1) because in the forward play there is no mate: 1.g8=Q? Bd1! The three-move preparatory plan will add the needed black plug on b3.
Finally, the "No Forward Defense" specification is needed against 5...Ra2-a1+ & 1...Re1#
An excellent composition, full of subtle motivations.
1.Kg2-h1 f4-f3+ 2.a5xb6 ep.(+wPb2) b7-b5 3.Kf1-g2 Rd8-d1+ 4.Ke1-f1 f3-f2+ 5.Kd1xRc1(+wKe1) 0-0-0+ 6.g7xSh8=S(+wSg1) & 1.g8=R#
In the initial position White is already under the threat of the forward defense 1...Qh7#, which explains the non-specific key.
The en passant capture has again a multiple purpose: it interferes with bBc6 on its way to a8, preventively obstructs bRa8 from delivering the forward defense 1...Ra2# after the castling and blocks the flight b7 with a black pawn.
Only a bS can be uncaptured on h8, because a bB would be able to parry the mate in the forward play with 1...Bxe5 [+bBf8].
Another splendid conception!
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.
1.Kc1-d2 a2-a1=S 2.0-0-0+ a3-a2 3.c5xb6 ep.(+wPb2) b7-b5 4.Kc8xRd7(+wKe1) & 1.Re1+ Rxg4(+bRa8)#
All the play is centered around zugzwang. The key forces unpromotion by means of stalemate, as after 1...Sc2-a1 there is no legal retraction for White. The purpose of the white castling is to specifically block a1 parrying the black King check.
Decapturing en passant with 3.a5xb6 ep.(+wPb2) is not possible because of the doubled pawns on file 'a' wPa5-bPa2, a setting that is illegal in AntiCirce. The purpose of the en passant capture is again to block the future flight b7.
Of course, in the forward play neither bB nor bK can capture wRg4, as c8 is blocked by the wK and e8 guarded by wR.
The above examples showed Valladao using AntiCirce. It is also possible to mix Proca Retractor with other fairy conditions, as in the next example.
1.g5xf6 ep.(+bPf7) f7-f5 2.Sd3xRb4(+bRh8,-bBh8) Rd4-b4+ 3.Ka2xpb2(+bPb7) Rd8-d4+ 4.Kb1xSa2(bSg8,-wSg8) 0-0-0+ 5.g7-g8=S b3-b2 6.Sb2xRd1(+bRa8,-bQa8) d2-d1=R+ 7.Rf3xpf7(+bPf7,-wRf7) & 1.Re3+ Qe4#
The thematic key opens both the diagonal h8-b2 and the line f3-f7. When wK stands on a2, bR may not attack any white pawn standing on the 'a' file and is forced to retreat to d8. Black castling is forced thanks to a double check delivered by bR on both wSd3 and wSg8. A similar motive appears later forcing the promotion of the bR.
However, the most interesting point in the solution is the surprising zugzwang appearing after the white promotion, with bR and bK not able to move as they have just castled and bSa2 being specifically tied up.
Although being passive throughout the whole retro play, the wQ specifically guards the flights d7 and d8 during the forward play, while the bQ delivers the mate and specifically guards a1.
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.