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Subject: Re: The next WCCC ....

Author: Simon Finn

Date: 17:19:28 11/13/99

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On November 13, 1999 at 18:47:31, Simon Finn wrote:

>If it can pass "lost in N" on the Mth iteration, then it knows
>that DTC <= M. That's enough (for M = 50) to implement the 50
>move rule.

Whoops - that's slightly wrong, because the white-to-move and
black-to-move positions aren't computed simultaneously.

After the M'th iteration, we get:
   DTC <= 2*M   half-moves (for white-to-move) and
   DTC <= 2*M+1 half-moves (for black-to-move)

(Or are the colours reversed? It's too early in the morning
to start worrying about that now.))

So after 50 iterations, the white-to-move tablebase is correct,
but the black-to-move tablebase is off-by-one (and therefore useless).

Fix: run the algorithm twice, with colours reversed, and
discard the two off-by-one half-tablebases.

Simon





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