Dual avoidance

Partial dual avoidance. Avoided dual is a mate/maneuver which is prevented in one and realized in another phase.The mate effective in one variation is prevented in another and vice versa. This type can with good reason also be termed "Reciprocal Dual Avoidance". However, other scenarios are possible, such as for instance cyclic dual avoidance.

Total dual avoidance. The prevented mate/continuation appears as a possibility only once and doesn't become effective in any other phase.

Another criteria is the location of thematically relevant effects, i.e. whether they are contained in a defence or in a mate:

Active dual avoidance: Black move/maneuver carries a negative effect which prevents a dual mate/continuation.

Passive dual avoidance: it seems that one side has a choice of moves to achieve the required effect but in each such case there is a single reason (negative effect) why every move but one fails.

See also: Stocchi blocks.

Medintsev, Vitaly

KoBulChess, 2013 (v)

3rd Prize

Example: Dual avoidance
h#2 2.1... (6+4)

1.Scb6 Rg4 2.Sb4 Ra1#
1.Sdb6 Rg5 2.Sa5 Rb1#

1.Scb6! (Sc~?) Rg4 2.Sb4! (tempo) Ra1#
1.Sdb6 (Sd~?) Rg5 2.Sa5! (tempo) Rb1#

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FEN: 1B4K1/b7/8/R2n4/1Rn5/7P/4P3/7k

External links:

Gurov, Valery

Probleemblad, 2001

1st Prize

Example: Dual avoidance
h#2 3.1... (11+10)

1.Qxd2 b6 2.Sxa5 Sb5#
1.Qxa5 f5 2.Sxd4 Bf4#
1.Qxd4 a7 2.Sxd2 Ra6#

1.Qxd2 b6 (a7? 2. Sxd2?? Ra6#) 2.Sxa5 Sb5#
1.Qxd4 a7 (f5? 2. Sxd4?? Bf4#) 2.Sxd2 Ra6#
1.Qxa5 f5 (b6? 2. Sxa5?? Sb5#) 2.Sxd4 Bf4#
Cyclic partial active dual avoidance.
B1: positive effect: unpin, negative effect: square obstruction.

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FEN: 8/1R6/P2k1pp1/RPpP2P1/p2N1P2/Knq5/B1rB4/r1n5

External links:

Shorokhov, Boris

Turevsky, Dmitry

The Problemist, 2013

Example: Dual avoidance
h#2.5 2.1... (7+13)

1...Bxf7 2.Bd2 Bxg6 3.Qxb7 Bxh5#
1...Sxd6 2.Sd2 Sb5 3.Rxe6 Sxc3#

1...Bxf7 (1...Bxf5?) 2.Bd2 (2.Sd2?) Bxg6 3.Qxb7 Bxh5#
1...Sxd6 (1..Sc5?) 2.Sd2 (2.Bd2?) Sb5 3.Rxe6 Sxc3#
Partial passive dual avoidance in B2:
Positive effect: self-blocking, negative effect: guard.
AntiZielElement (B2, line-opening).
Choice of white moves in W1 (not dual avoidance).

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FEN: 3K4/1N3p1q/1prpB1pb/3P1p1p/2n1P2P/2pN4/2p5/3k4

External links:

Bakcsi, György

Probleemblad, 1962

2nd Prize

Example: Dual avoidance
h#2 3.1... (7+12)

1.Rf3 Se5 2.Sxe7 Sg4#
1.Sf3 Sd4 2.Sf6 Sf5#
1.f3 Sb4 2.Sh6 Sd5#

1.Rf3 Se5 (Sb4?, Sd4?) 2.Sxe7 (Sh6?, Sf6?) Sg4#
1.f3 Sb4 (Sd4?, Se5?) 2.Sh6 (Sf6?, Sxe7?) Sd5#
1.Sf3 Sd4 (Se5?, Sb4?) 2.Sf6 (Sxe7?, Sh6?) Sf5#
Cyclic triple avoidance.

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FEN: K5n1/4P3/2N1P3/8/3n1p2/1p1Pk2p/1P1b1rbp/5Brq

External links:

Feather, Christopher John

Quartz, 1998

Example: Dual avoidance
h#2 3.1... (4+7)

1.Sd5 Qh2 2.Rb7 Qd6#
1.Sf5 Qg1 2.Rd7 Qb6#
1.Sc8 Qh5 2.Rc7 Qb5#

View in Helpmate Analyzer

FEN: 6b1/4nr2/n1k3p1/8/2N5/1pN5/6K1/7Q

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