Bi-Valve

Theme Bivalve : The black, opening a line of one black piece, closes another line of another black piece.

	(Problem 73) B. G. Mansfield, First Prize, ”Olympic Tourney”, 1936 White plays and mates in 2 moves #2 (6+11)
[8/KS5b/pR6/8/k1p1Q2r/4s3/PPp5/3r1sbq]

Tries: {1.Sc5+? Ka5!}, {1.Rb4+? Kxb4!}, {1.Qc6+? Qxc6!}, {1.Qe8+? Rd7!}, {1.b3+? Ka3!}.
Key: 1 a3! [2.Rb4#]
The threat is neutralized by lifting Se3 on air, because Bg1 pins Rb6, but on which square will the black Knight come down?
1...Sg2 2.Qc6# (one line of Qh1 has been closed)
1...Sg4 2.Qxc4# (one line of Rh4 has been closed)
1...Sf5 2.Qxc2# (one line of Bh7 has been closed)
1...Sd5 2.Qe8# (one line of Rd1 has been closed and one line of Qh1 has been closed)


In the prized problem-74, product of the cooperation of the great composers Loshinsky and Umnov, we see that Black tries (playing differently) to correct his defense (=black correction), and then tries to correct again (=secondary correction), and then tries to correct again (=tertiary correction), but eventually he becomes checkmated.

	(Problem 74) L. I. Loshinsky – E. Umnov, First Prize, ”Western Morning News”, 1930 White plays and mates in 2 moves #2 (9+8)
[B4K2/4pQ2/6p1/2p1kS2/6r1/2SRsbP1/1B3q2/4R3]

Tries: {1.Kxe7? / Bd5? Qxg3!}, {1.Qd5+? Bxd5!}, {1.Rd5+? Bxd5!}, {1.Qe6+? Kxe6!}, {1.Qxe7+? Kxf5!}, {1.Sxe3? / Rdxe3+? / Rexe3+? Qxe3!}, {1.Se2+? Rd4!}, {1.Se4+? Qxb2!}.
Key: 1 Sh6! [2.Qxe7#].
When Bf3 is lifted on air the threat is neutralized, because a line of Qf2 opens and the Qf7 is pinned, but on which square will the black Bishop come down?
1...Bh1 2.Sxg4# (Rg4 has been left unprotected)
1...Bd1 (black correction, protects Rg4, but Se3 has been left pinned) 2.Rd5#
1...Be4 (secondary black correction, does not protect directly Rg4, but unpins Se3 which guards g4. The bishop however closes the line of Rg4 (bi-valve) towards d4) 2.Se2#
1...Be2 (tertiary black correction, supports Rg4 and unpins Se3, closes however the line of Qf2 (valve) towards Bb2) 2.Se4#


[This post in Greek language].