Puzzle 3 – A proof game

December 27, 2010

Now we move into a different world with the type of puzzle
called a proof game. In this type of puzzle, you are given
a position on the board and the move number at which it
arose. You have to work out how, from the usual starting
position, the given position could have arisen in the requisite
number of moves.

a) Proof game in 6.5 moves
b) Proof game in 7.5 moves

This problem has two parts. In the first part, you have
to work out how the diagram position could have arisen after
White’s 7th moves in a normal game of chess. Note
that the moves don’t have to be good or even sensible,
they just have to be legal. In the second part, you have
to work out how the position could have arisen after White’s
8th move. At first this seems ridiculous, for if the position
can arise after White’s 7th move, there wouldn’t
seem to be any problem arranging for it to arise after White’s
8th move. However, when you think about it you’ll
see that there’s a special reason why the second part
is not trivial.

One hint is to bear in mind that in each part the solution
is absolutely unique. This enables you to eliminate many
possibilities; for example, Black’s first two moves
can’t be 1…d6 and 2…Nc6, because he could just
as well have played 1…Nc6 and 2…d6.

John Nunn

Please do not send in any answers yet – just
keep notes of your solutions. We will ask for them at the
end of the puzzle sessions. The prizes themselves will be
announced in the course of the Christmas Puzzle week.