Chess Problems: Solutions to the Obstruction problems

6/12/2012 – In his last column David Friedgood explained the concept of "obstruction" – which occurs when a piece moves to a square so that another piece is prevented from occupying it. He gave us examples that showed the basic idea and two three-movers to solve. Noam Elkies, a Harvard maths professor and himself a composer and solving GM, commented succinctly on the second example: 'Hilarious!'

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Chess Problems solutions!

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.

The solutions to the two problems set in my latest article on the theme of Obstruction are given below. I trust that they were not too difficult even though they are three-movers.

[Event "5th Prize, Die Schwalbe"] [Site "?"] [Date "1950.??.??"] [Round "?"] [White "Siegfried Brehmer"] [Black "Mate in 3"] [Result "*"] [Annotator "David Friedgood"] [SetUp "1"] [FEN "b6k/2B5/4Np1K/8/4p3/2n3R1/8/8 w - - 0 1"] [PlyCount "5"] [EventDate "1950.??.??"] 1. Rg6 $1 {is the key (White's threat is as below), but first note how White's more obvious attempts to force mate fail:} (1. Bd8 $2 Nd5 {and now White can't take advantage of the obstruction of the Ba8, as 2.Nd8 is impossible, the square having been obstructed by the white bishop!}) ({Similarly, after} 1. Nd8 Bd5 {White can't exploit the obstruction of d5 with 2.Bd8, as d8 is again obstructed!}) 1... Nd5 ({Threat:} 1... -- 2. Rxf6 {and there is no stopping} -- 3. Rf8#) (1... Bd5 {, aiming to meet} 2. Rxf6 {with 2...Bxe6, now obstructs the black knight preventing ...Nd5, so that} (2. Bd8 {forces} -- 3. Bxf6#)) 2. Nd8 {and Black no longer has the resource 2...Bd5 to prevent the now inevitable } -- 3. Nf7# {A fine demonstration of mutual obstruction, between not only black pieces, but white ones as well. A memorable little classic, prized for its outstanding economy.} *

[Event "Mat"] [Site "?"] [Date "1981.??.??"] [Round "?"] [White "Milan Vukcevich"] [Black "Mate in 3"] [Result "*"] [Annotator "David Friedgood"] [SetUp "1"] [FEN "4K3/5p2/4PP2/4p3/p1p4p/kpPb1p2/rnp2P2/b1B4Q w - - 0 1"] [PlyCount "5"] [EventDate "1981.??.??"] {My clue for solving this problem was to identify the black piece that needed to be obstructed. It is clearly the knight, because if the white bishop moves away to e3 or h6 threatening mate on c5 or f8, then the knight can move to d1 (all the other squares are blocked), vacating a flight square for the king. Together with my other hint - that this was in the nature of a puzzle - you should have been able to arrive quite quickly at the blockbusting key} 1. Qd1 $3 {The motivation for this move is made clear in the threat below.} fxe6 {is a non-thematic variation which just allows a version of the threat:} ({Threat: } 1... -- 2. exf7 -- (2... Bg6 3. Qd6#) 3. f8=Q#) (1... cxd1=N {Now the Nb2 is not merely obstructed on d1, it is completely paralysed, allowing the white bishop to unpin it and move out of reach of the promoted knight:} 2. Bh6 {, forcing mate on f8}) (1... cxd1=Q {Again the knight is paralysed. The white bishop is therefore no longer required to pin it and can move away to threaten unpreventable mate by} 2. Be3 {forcing mate by 3.Bc5.} ({Not} 2. Bh6 $2 {, as any move of the Bd3 enables the queen to interpose on d6.})) 2. f7 Bg6 (2... -- 3. f8=Q#) 3. Qd6# {This problem is a delightful demonstration of paralysis, which is a special case of obstruction. I shall return to this theme in my next article.} *

Noam Elkies is a Harvard maths professor and also a solving GM and composer of problems and endgame studies. His comment on this problem was simply: “Hilarious!”

Any queries or constructive comments can be addressed to the author at

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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