Chess Problems: The Half-pin Theme
By David Friedgood
The concept of the half-pin is quite simple: “Two units are said to be
half-pinned [against the king] when one of them becomes completely pinned when
the other moves.” (John Rice, “Chess Wizardry: The New ABC of Chess
Problems”, B.T. Batsford 1996). The half-pin theme intensifies the richness
of the solving experience. It combines well with many other themes and motifs,
providing fertile ground for composers for well over a century.
[Event "Good Companions"] [Site "?"] [Date "1921.??.??"] [Round "?"] [White
"K.A.K. Larsen"] [Black "Mate in 2"] [Result "*"] [Annotator "Friedgood,David"]
[SetUp "1"] [FEN "R4b2/1Kp3p1/8/1kN5/8/1r6/NnQ5/1R6 w - - 0 1"] [PlyCount "3"]
[EventDate "1921.??.??"] 1. Nd3 {Threatening 2.Qc6#. The thematic variations
are: 1...} Nc4 {(continued in main line)} (1... Rc3 2. Qa4# {The move of the
rook has opened the way for the queen to mate, depending on the fact that the
black knight is now pinned and has lost control of a4.}) ({Non-thematic variations
are:} 1... c5 2. Qxb3# {taking advantage of the interference of the bishop by
the pawn, which stops it from interposing on b4.}) (1... Bc5 2. Qxc5#) 2. Nc3#
{Depending on the fact that Black's rook is now pinned by the Rb1 and also by
the self-blocking of c4, allowing the knight to interfere with the queen in
delivering mate.} *
The first problem is a simple introduction. The half-pin structure is already
visible on the b-file: when the black rook or knight moves off this file the
other becomes pinned by the b1 rook. All we have to do to activate the half-pin
variations is to find the key move that will provoke the thematic defences.
The second problem shows a masterly treatment by a great exponent, combining
the half-pin with self-block, line-opening, interference, and unpin.
[Event "1st Prize Hampshire Telegraph and Post"] [Site "?"] [Date "1919.??.??"]
[Round "?"] [White "Comins Mansfield"] [Black "Mate in 2"] [Result "*"] [Annotator
"Friedgood,David"] [SetUp "1"] [FEN "8/8/2P1Q3/B2R4/r1k1n2r/pNn4p/B1qP3K/N1R2b2
w - - 0 1"] [PlyCount "3"] [EventDate "1919.??.??"] {The good key is} 1. Qf5
$1 {paradoxically giving up the Q+R battery pointing at Black's king in order
to cover b5 in preparation for the threat 2.Rd4#. The thematic variations involve
defences by the half-pinned pieces on c2 and c3: 1. ..} Ne2 {protecting d4 makes
no less than 3 "defensive errors": it causes Black's queen to become pinned,
unpins the Pd2, and interferes with the Bf1, all of which are necessary to enable
White to mate by...(continued as main line)} (1... Nxd5 {is the next defence,
this time making just one defensive error in addition to the pinning of the
black queen: the self-blocking of the d5 square, enabling the white queen to
release control of it in order to mate by} 2. Qxf1#) (1... Nb5 {is our third
thematic defense, this time the additional error being the self-blocking of
b5. Now the bishop+knight battery can open and deliver mate by} 2. Nc5# {self-interfering
with the rook. The clever point here is that the knight had only c5 and d4 to
choose between, all other destinations being occupied by friendly forces. d4
would have been the wrong choice, as it would have interfered with the rook's
control of d3 and provided the black king with a flight square.}) (1... Qd3
{is the queen's single thematic defence, and it shows the other side of the
coin to 1...Nb5. Now the c3 knight becomes pinned, losing control of the B+N
battery, and this time the queen self-blocks on d3, enabling the knight to choose
the d4 square rather than c5 as its destination:} 2. Nd4#) ({Non-thematic defences
include:} 1... Qxd2+ 2. Nxd2# {with mate by double-check}) (1... Qxb3 2. Bxb3#)
({Any move of the e4 knight defends by opening the line of the rook on h4 to
the d4 square, but this unguards c5 as well as opening the line of the queen
to protect d3, allowing e.g.} 1... Ng5 2. Rc5#) 2. d3# *
The last two diagrams are for the reader to solve. In each case, you have to
find the unique key move for White, after which Black is unable to avoid mate
on the second move regardless of what the defender plays. In both cases the
half-pin is easy to spot and the variations are relatively simple, but the keys
are quite crafty. As a hint to the inexperienced solver, I would mention that
the key of a problem does not necessarily carry a threat.
Mate in two moves
Mate in two moves
Solutions will appear in approximately one week.
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
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The Society produces two bi-monthly magazines, The Problemist and
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