Chess Problems: Obstruction!

by ChessBase
5/29/2012 – In his last column problem expert David Friedgood explained the self-block, which is a special case of today's theme: obstruction. This occurs when a piece moves to a square so that another piece is prevented from occupying it. We are given two examples that show the basic idea – one with three beautifully engineered variations – and two problems to solve. An entertaining challenge.
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Chess Problems: Obstruction!

By David Friedgood

“Obstruction occurs when a piece moves to a square so that another piece is prevented from occupying that square” (Chess Wizardry: The New ABC of Chess Problems, by John Rice, B.T. Batsford 1996). It is clear from this definition that the self-block, which my last series of articles explored, is really a special case of obstruction, in which a flight square in the king’s field is blocked. In a two-mover, the self-block of the king is the only type of obstruction that is feasible, so we will be dealing with three and more-movers from now on.

Let us look at some problems exemplifying obstruction. The first shows the basic idea repeated in three beautifully engineered variations on the theme:

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The key is 1.Kd7 This move guards d6 in preparation for the threat (see details below). Qb1 1...-- Threat: 2.Qg6+ Ke5 3.Nxd3# All Black can do to defend is to protect d3, for which there are three queen moves available, 1. ..Qb1 (see main line)/Qb3/Qc4. These moves might appear quite innocent and undamaging to Black, but the composer has arranged a devilish trap for each one 1...Qb3 2.Nfxe6! -- ∆3.Nc5# ∆3.Qf4# Black is unable to cope with this double threat. The Nd2 needs to move away to allow the Bc1 to protect f4 for the Qf4 threat, but since b3 is now blocked, that square is unavailable to the knight simultaneously to protect c5 against the Nc5 threat. 1...Qc4 2.Ng6! -- 3.Qe5# 3.Qf4# This time Black can't defend e5 as well as f4, because 2...Nc4 has been rendered impossible by Black's first move, which obstructed that square. 2.Nfxd5! -- ∆3.Nc3# ∆3.Qf4# The double threat forces mate as 2...Nb1 is impossible. This clever problem thus shows three obstructions of a knight by the queen.
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Michael Keller-Mate in 3-19681st Prize Schweiz. Arb. Schachzeitung

The second problem, a four-mover, shows mutual obstruction on the same square between two pieces, harking back to the similar Grimshaw theme:

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Solution: 1.Qh1 See details of the threat below. Rb5 This allows Black to interpose the rook on f5 after 2.f3+ Ngxf3 3.Qh7+ preventing mate on the fourth move. Threat: 1...-- 2.f3+ Ndxf3 2...Ngxf3 3.Qh7+ 2...Kxf3 3.Rxd2+ 3.Qb1+ Kxe3 4.Re2# or 4.Qd3# 1...Bb5 This allows the bishop to prevent 4.Qd3#/Re2# after 2.f3+ Ndxf3 3.Qb1+ Kxe3! 2.Rh2+ Ngf3 2...Ndf3 3.Qb1+ Bd3 4.Qxd3# 3.Rh8! A second Bristol! -- ∆4.Qh7# This time the mate threat can't be countered by Black as 3...Rb5 is impossible. 2.Rg1+! Ndf3 2...Ngf3 3.Qh7+ Rf5 4.Qxf5# 3.Ra1! The famous Bristol manoeuvre: the rook clears the line for the queen by moving along the line beyond the square to which the queen will move. -- ∆4.Qb1# The mate threat can't be countered by Black as 3...Bb5 is impossible. A brilliant setting of the obstruction theme, combined with the Bristol manoeuvre doubled. The problem shows the mutual obstruction between rook and bishop on the same square, reminiscent of the Grimshaw theme [the mutual interference on the same square between rook and bishop - also bishop and pawn] . Note how White's second move in the thematic variations paradoxically interferes with the queen. The mechanism of this problem will repay careful study.
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Milan Vukcevich-Mate in 4-19821st Prize Schach Echo

Now I leave you with two obstruction-themed problems for solving, the annotated solutions to which will appear in a while. In both cases you have to find the unique key move which contains a threat of forcing mate on the third move. You have to find Black’s defences to the threat and the continuations whereby White takes advantage of the new weaknesses arising from these defences.


    Mate in three

A simple problem where the key move provokes mutual obstruction between the black pieces. There is a bonus feature which you may well spot when you are solving the problem.


    Mate in three

This problem has a strong puzzle flavour. You’ll probably soon be home and dry once you spot which black piece needs to be obstructed.

Any queries or constructive comments can be addressed to the author at david.friedgood@gmail.com.

Copyright in this article David Friedgood 2012/ChessBase

The British Chess Problem Society (BCPS), founded in 1918, is the world's oldest chess problem society. It exists to promote the knowledge and enjoyment of chess compositions, and membership is open to chess enthusiasts in all countries.

The Society produces two bi-monthly magazines, The Problemist and The Problemist Supplement (the latter catering for beginners), which are issued to all members. Composers from all over the world send their problems and studies to compete in the tourneys run by the society.

The BCPS also organises the annual British Chess Solving Championship, and selects the Great Britain squad for the World Chess Solving Championship. The Society holds an annual residential weekend, with a full programme of solving and composing tourneys and lectures; this event attracts an international participation. Members are also entitled to use the resources of the BCPS library, and the Society book service, which can provide new and second-hand publications.

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