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Bristol
Peter's Problem World with FIDE Master of Chess
Composition
Peter Wong
New terms introduced here
are also added to Peter's
Glossary of Chess Problem Terms.
|
Many problem
themes focus on the power of long-range
pieces that act on lines, such as the
battery (lines are opened by discovery),
and the
Grimshaw (lines are closed due to
self-interferences).
Another strategic idea based
on line play is line clearance. Take two similar line-pieces
of the same color – 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.
This manoeuvre is known as a
Bristol clearance. |
|
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 and such
“purity of aim” may be seen as a desirable feature.
|
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…Ne4!. 1.Be5? provides for 1…Ne4 with 2.Qd4, but the bishop in
blocking e5 admits the
refutation 1…Be1! (since 2.Ne5 is now
illegal).
Two more tries hinder the white
rooks: 1.Bf6? Nb5! (2.Rc6 illegal), and 1.Bg7? Qf6! (2.Rc7 illegal).
The non-obstructive 1.Bh8!
is hence correct, giving 1…Ne4 2.Qd4, 1…Be1 2.Ne5,
1…Nb5 2.Rc6, 1…Qf6 2.Rc7, 1…c1(Q)/(N)+ 2.Qxc1, and
1…d4 2.Be6. |
68. Herbert
Ahues
Mat Theme
Tourney 1984
3rd Prize
       
       
       
       
       
       
       
       
Mate in 2 |
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