Author: Jesper Antonsson
Date: 02:01:42 07/27/02
I thought of a simple idea of EGTB optimization and I wonder whether it's been tried already. Imagine we have a position that is legal on the surface, but unreachable in a real game, like this one: [D]8/8/8/8/8/4k3/4p3/4K3 b - - 0 1 I believe standard EGTB calculation algorithms will store this as a mate in n for black, as Kf3 or Kd3 result in wins. Wouldn't it be beneficial to mark such positions as broken, so as to get better compression? It can obviously be done, even for "deeper" unreachable positions, essentially by iterating over the EGTB, but perhaps it requires information about illegal positions that aren't in current EGTB, and then a regeneration would be necessary. Note that for five men tables, just the example position above will come up in many variants with two more black pieces on the board. I have no idea of the ratio of such broken positions to legal positions, though, but it would be interesting to know.
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