Shortest Proof Games
– Part 1
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.
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The
shortest proof game (SPG)
is a type of problem in which the task is to reconstruct a legal game.
Starting from the opening array, the solver has to find the shortest
possible game that leads to the diagram position. White and Black thus
effectively cooperate to arrange this, and that the moves would not be
sensible in a competitive game is considered irrelevant.
SPGs are also characterised by their exact play – the move order in each
solution is unique (otherwise the problem is unsound). This requirement for
a single move order may itself serve as a pointer to the correct sequence,
and the precise play also contributes to a problem’s artistic quality. |
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The
stipulation of a SPG gives the length of
the solution in pairs of single moves. In Problem 97, for
example, “SPG in 9” indicates the position is reached after Black’s
9th move.
Solving a SPG typically begins
with a count of the number of “visible” moves made by the pieces no
longer on their starting squares.
Here, White’s queen, bishop,
and two pawns have used up at least four moves, leaving five moves for
other purposes. Black took five moves to promote the f-pawn, and the
new queen spent the remaining time to capture White’s missing pawns.
Because of the obstructing
white pawn on the f-file, the black pawn must have promoted on e1,
after capturing White’s knight on e2. The promotion also obliged the
white king to move out of the way, and the only viable method was a
surprising castling-and-return manoeuvre. |
97. Markus
Ott
Thémes-64
1981
1st Hon. Mention
       
  
 
 
    
SPG in 9 |
1.e4 f5 2.Bd3 f4 3.Ne2 f3 4.0-0 fxe2
5.f4 e1(Q) 6.Qe2 Qxd2 7.Kf2 Qa5 8.Rh1 Qxa2 9.Ke1 Qf7.
1.e3 h5 2.Qxh5 a6 3.Qd1 Rxh2 4.Bxa6 Rh8 5.Rxh8 Nf6 6.Rxf8+ Kxf8 7.Bf1 Ke8.
Four pieces execute switchbacks to their original squares, viz.
White’s queen and bishop, and Black’s king and rook.
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In Problem 99, most of
White’s moves and their order are fairly obvious from the diagram: Pe3,
Ba6, Pc4, and then Qa4. That leaves White two spare moves to sacrifice
the missing pawn and bishop to an opposing knight.
Implementing this plan proves to
be difficult, however, because Black’s knight from g8, after making the
two captures, has insufficient time to get captured itself, e.g. 1.d4
Nc6 2.Bh6 Nxh6 3.e3 Nf5 4.Ba6 Nfxd4 5.c4 Nb8 6.Qa4 Nd-?.
The answer is to sacrifice the
knight from b8 instead, followed by its replacement by the “sibling”
piece: 1.d4 Na6 2.Bh6 Nxh6 3.e3 Nf5 4.Bxa6 Nxd4 5.c4 Nc6 6.Qa4 Nb8. |
99. Michel
Caillaud
Problemesis
2001
SPG in 6
(b) Nb8 to g8 |
The
thematic
twinning shifts the knight back to g8,
creating another SPG position. Amusingly enough, the second part sees an
encore of the change-to-sibling scheme, but done in reverse: 1.d4 Nh6
2.Bxh6 Nc6 3.e3 Nxd4 4.Ba6 Nf5 5.c4 Nxh6 6.Qa4 Ng8.
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100.
Richard Müller
Rochade
1985
SPG in 6.5 |
Problem 100 calls for a
SPG in 6.5, indicating the diagram is attained after White’s 7th move.
Both sides are missing only two
pieces, but straightforward attempts to remove them would not work, e.g.
1.e4 d6 2.Ba6 Bf5 3.Bxb7 Bxe4 4.Bxa8 Bd5 5.Bb7 Bxa2 6.Ba6 Be6 7.Bf1 Bc8
– a single move too long.
The absent a2-pawn, b7-pawn and
a8-rook, from adjacent files, are a telltale sign that White may have
promoted, so let’s begin with 1.a4 d6 2.a5 Bg4 3.a6 Bxe2 4.axb7,
and now if Black were to try to capture the (soon) promoted piece, the
play would still take too long, e.g. 4…Bf3 5.bxa8(Q) Bxa8 6.Nh3 Bb7
7.Ng1 Bc8. |
Instead, Black
has to capture something else – a piece that White can replace by promotion,
4…Bxd1 5.bxa8(Q) Bg4 6.Qf3 Bc8 7.Qd1. This is called the
Pronkin theme: the substitution of a captured piece on its initial
square by a promoted counterpart.
Return to Peter's Problem World
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