No.1541 (PAP & GF)

(C+ by Popeye 4.85)

Solutions:
(a) Thematic try in logical style: 1...Bb5? 2.Be6 and now 2...Qg8?? is impossible because the a2-g8 diagonal has been closed by the wB. Correct is: 1...Qg8! 2.Be6! Bb5 3.Bb3 Sf7+! 4.Ke6+! Sd6#.
(b) Thematic try in logical style: 1...Qb3? 2.Bd7 and now 2...Be8?? is impossible because the a4-e8 diagonal has been closed by the wB. Correct is: 1...Be8! 2.Bd7! Qb3 3.Bb5 Sd7+! 4.Kc6+! Sc5#.

Themes:
1. Black Indian theme Q/S and B/S with cross-check finales given by the white K/B battery and the black Indian batteries.
2. The critical moves of the Indian theme 1...Qg8! and 1...Be8! are also anti-critical moves concerning the white Bg4, which after 2.Be6 ~ 3.Bb3 [in (a)], and 2.Bd7 ~ 3.Bb5 [in (b)], moves in the opposite direction to the black piece.
3. An additional element in the play of Bg4 is that its first move is a “Bivalve”, opening a line to pin the bBf4 while also closing a black line.
4. The logical tries at the beginning close lines needed by the thematic black pieces.
5. Interchange of functions between black Qa2 and Bc6 – when one of these pieces makes a critical move, the other piece blocks a square around the bK.