Saturday, April 26, 2008

Wurzburg – Plachutta intersection

Theme Wurzburg – Plachutta intersection : two black pieces with similar linear movement mutually interfere (mutual Holzhauzen interference) on the same square.
If the pieces are white, we have white Wurzburg – Plachutta intersection.

The theme first appeared in 1909, and it needs at least 3 moves.
In one variation, with the first move we force a black piece-A to interfere to a similar black piece-B. On the second move we lure piece-A to play the role of piece-B. On the third move we achieve our goal.
In another variation, piece-B interferes to piece-A, piece-B is lured, and then we give mate.
The piece that arrives on the square of interference assumes the duty of guarding two squares and we say that it is overloaded.

(Problem 67)
Jan Hartong,
First Prize, ”Tijdschrift v. d. Nederlandse Schaakbond“, 1943
White plays and mates in 3 moves
#3 (8+11)

Tries: {1.Qxc5+? Sxc5!}, {1.Qxd7? Rxd7!}, {1.exd5? Re6+!}, {1.Bxd3+? Rxd3+!}.
Key: 1.Bd2! [2.Qxc5 Rxc5 / Sxc5 3.Bxd3# / Sb2#] (The Queen Qe7 must not reach c5).

There are two thematic defenses:
(a) 1...Rad6 2.Qxd7 [3.Qb5#], (and now...)
2...Rc6 / Bc6 3.Qxd5# / Sb6# (because Ra6, which must guard b6, has passed over the critical square c6 and this became a black Grimshaw intersection)
or 2...R6xd7 (there is not R5xd7) 3.Sb6#

(b) 1...Rdd6 2.Qf6 ([3.Qc3#], (and now...)
2...Rd4 / Se5 2.Qxa6# / Sb2#
or 2...Rdxf6 (there is not Raxf6) 3.Bxd3#

Let us see two non thematic defenses:
(c) 1...d5 2.Qe5 (the rook is pinned and there is a threat Bxd3. If Sd3 plays, allows 2.Sb2, and the continuation is ...) 2...b2 3.Ba2#

(d) 1...fxe4 2.Qxe4+ Rd4 3.Bxd3# (without interesting play).

In the more recent problem-68, by Chepizhni, we see Wurzburg – Plachutta interferences with changed play in three phases.

(Problem 68)
Viktor Ivanovich Chepizhni,
First Prize e.a., ”40th Anniversary Tourney, Shakhmatny v. SSSR”, 1966
(There is set play). White plays and mates in 3 moves
* #3 (9+11)

Phase of set play: (*)
1...Bc3 2.Rb4+ Bxb4 3.Se5# (mate A)
1...Qc3 2.Rd4+ Qxd4 3.Sa5# (mate B)

Phase of virtual play: Try: {1.Kb6? [2.Qc8 [3.Sc~]] Sxc2!
1...Bc3 2.Rb4+ Bxb4 3.Se5# (mate A)
1...Qc3 2.Se5+ Qxe5 3.Rb4# (mate C) }

Some more tries: {1.Qf8? d6!}, {1.Qc8? Sxc2!}, {1.Sa5+? Qxa5+!}, {1.Se5+? Bxe5+!}, {1.Rd4+? Bxd4!}, {1.Rb4+? Qxb4!}.

Phase of actual play: Key: 1.Kd6! (same threat 2.Qc8, forms battery with Sc6)
1...Bc3 2.Sa5+ Bxa5 3.Rd4# (mate C)
1...Qc3 2.Rd4+ Qxd4 3.Sa5# (mate B)
1...Sc2 2.Sa5+ Qa5 3.Qd5#

We have noted, inside parentheses, with (A, B, C) the mates that follow the moves (Bc3, Qc3), in order to show their combinatorial change : (AB, AC, CB).

Now, about the solving method, an experienced solver, observing the initial setting of the pieces, he/she could think in the following way:
The position is almost symmetrical and the composer wants Ba1 (which stops Se5) and Qe1 (which stops Sa5) to mutually interfere on c3, which becomes Wurzburg – Plachutta intersection.
Since Se6 (which holds c5) can be easily captured to create a flight for Kc4, probably Kc7 comes closer. From which direction does the King approach?
If we plan to play Kb6 as key, the Queen Qe1 can not play Qe3 to check. The composer, who put Bishop on a1 and Queen on e1 (Ba1 and Qe1), could equally have put Queen on a1 and Bishop at e1 (Qa1 and Be1), but why did he choose the former?
A possible explanation : If the correct key-move is Kd6, then a Queen on a1 could capture pawn a3, give check and ruin the solution.
From that point on, the solver discriminates which is the try and which is the key and solves the problem.

[This post in Greek language].

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