Bristol

Many problem themes focus on the line effects produced by long-range pieces, such as the battery (lines are opened by discovery), and the Grimshaw (lines are closed due to self-interference). Another strategic idea based on long-range play is line clearance. Take two similar line-pieces of the same colour – e.g. two rooks, or a queen and a bishop – and move one of them along a line so that the other can follow along the same line. The first piece ‘clears’ the line for the second and, in particular, crosses over a critical square which becomes accessible to the following piece. Such a manoeuvre is called a Bristol clearance.

Problem 67 is the famous three-mover that originated the idea. (The theme acquired its name after this composition gained a first prize in a tourney held in Bristol.) In the diagram, some of Black’s moves have short mates in one move set for them, 1…S-any 2.Qd6 and 1…Ba6/Bc6 2.Qc6, but White has to deal with the unprovided 1…Bd7/Be8. The only way is 1.Rh1! (waiting), a spectacular key that passes over the critical square g1. Now 1…Bd7/Be8 is answered by 2.Qb1 (threat: 3.Qb4) Bb5 3.Qg1. The key-rook in this problem serves no function other than to clear the first rank (it becomes redundant after the move), making this a pure rendering of the Bristol theme. Though a principle of good problem construction holds that each piece should be utilised fully, preferably by having more than one function, a line-clearing piece is an exception to this rule; it exemplifies instead the feature of “purity of aim”.

In Problem 68, the white bishop on the long diagonal makes a series of impure, but thematic, Bristol tries. The clearances are not completely pure because the bishop, in crossing c3 to threaten 2.Qc3, also acts as a guard on that square. The first try, 1.Bd4?, fails to 1…Se4! 1.Be5? provides for 1…Se4 with 2.Qd4, but the bishop in blocking e5 admits the refutation 1…Be1! (since 2.Se5 is now prevented). Two more tries hinder the white rooks: 1.Bf6? Sb5! (2.Rc6 illegal), and 1.Bg7? Qf6! (2.Rc7 illegal). The non-obstructive 1.Bh8! is hence correct, yielding 1…Se4 2.Qd4, 1…Be1 2.Se5, 1…Sb5 2.Rc6, 1…Qf6 2.Rc7, 1…c1=Q/S+ 2.Qxc1, and 1…d4 2.Be6.

In Problem 69, the key 1.g4! gives a thematic threat that nicely complements the main variations. The threat is the clearance 2.Ra8 and 3.Qb8. Black defends by activating the b2-bishop, aiming to interpose the piece on d6 via a3 or b4. Three such defences enable White to create more Bristol play along the e-file. 1…Rb3 shuts off the a2-bishop and allows White to play 2.Re4 and 3.Qe5, since 2…dxe4 no longer checks White. (In all variations, the black knight is paralysed by the need to prevent Sgf3 mate.) 1…Rc3 interferes with the other bishop and permits 2.Re3 and 3.Qe5, since now 2…dxe3 is useless against the queen mate. Lastly 1…Bc3 cuts off the black rook, allowing 2.Re2 because once again the capture of the rook, 2…dxe2, no longer stops 3.Qe5.

Typically in a helpmate with two phases, the play is unified through White playing analogously across the two solutions, and Black doing likewise. Problem 70, however, achieves harmony in a different way: the matching play across the two solutions is executed not by the same player, but once by White and once by Black. Part (a) of this twin is solved by 1.Bf5 dxe6 2.Qe4 dxe7, and part (b) by 1.exd6 Rf7 2.exd5 Qe7. Thus in (a) Black carries out a Bristol and White makes a pair of pawn captures, while in (b) it’s White who carries out a Bristol and Black who makes a pair of pawn captures.

Every move appears as part of a Bristol manoeuvre in the highly intensive 71. The solutions are 1.Qe4 Rh1 2.Bf5 Qg1 and 1.Rf2 c4 2.R8f5 Rc3. Both white clearances are pure, including 1…c4 which illustrates the ability of a pawn, on its initial square, to act like a line-piece. In relation to the point made earlier about how well-constructed problems utilise the pieces fully, notice the functions of the thematic pieces when they don’t play the Bristol moves. The white pawn guards d3 in one solution, while the white queen guards e4 in the other. Each pair of black line-pieces, when stationary, are also essential for controlling the prospective white mate, to force the interference on f5.