On 16 Mar 2007 16:42:55 +0000 (GMT), David Richerby
wrote:

Mike Murray wrote:
If perfect play results in a forced win for White (the advantage of
the move proves decisive) or for Black (the initial position turns
out to be zugzwang), then the side with the disadvantage could play
perfectly and still lose.

If one side (let's say White) can force a win with perfect play and
proceeds to do so, it doesn't really make sense to ask if Black was
playing perfectly. A strategy is perfect if it obtains the best
possible result from any position. If White has a forced win, the
best possible result for Black from any position that White will allow
to occur is a loss (for Black) so any move, including `Resigns', is
`perfect'.

You could argue that losing in a hundred moves is preferable to losing
in three but that's pretty subjective -- there's nothing in the rules
that says that a quick win is in any way preferable.

In any position, most players would define "perfect" play in a lost
position as that posing the most problems for the opponent, giving the
opponent the most chances to go wrong. Your definition is fine if
one abstracts the element of competition from the problem, i.e., if
one assumes the opponent is capable of finding those perfect moves the
position demands, and can make these moves in the game within time
limits, etc. So, facing a choice of theoretically lost positions, a
GM forcing his opponent into one of the weird Queen endings for which
a forced mate in 144 (or some such thing) exists in the tablebases,
would be playing "better" than if he fell on his sword into a mate in
four, even though the outcome would be the same were he facing God or
Fritz XXX.

At any rate, since we were arguing against Houlsby's claim that "Every
lost position results from a decisive mistake. No decisive mistake, no
lost position, drawn game", my paragraph cold be rewritten as

"If perfect play results in a forced win..., then the side with the
disadvantage could make no errors and still lose."

which seems to finesse your objection.


Dave.