Q: Interpretation of TBS files

[h.g.muller]

I looked at the krnnkr.tbs and kqnnkq.tbs files posted on this website,to figure out if these end-games are generally won or not. But there is something I don't understand:

The files contain wtm lost/draw/won/broken and btm lost/draw/won/broken position counts. But when I add them up, the number of wtm and btm positions is different. I always thought that 'broken position' meant two pieces on the same square. But that should not depend on who has the move.

So what do the 'broken position' counts in those files actually mean, and what positions are not included in the counts so that wtm and btm totals can be different?

[syzygy]

I suppose broken includes positions wherein the side to move can capture the opponent's king.

[h.g.muller]

That could explain why the are different for the two stm. But then I don't understand how the total of won + lost + draw + broken could be different for wtm and btm. That should just be 64^N (times whatever factor you get from symmetry reductions).

[mbourzut]

The Nalimov "broken" positions exclude certain illegal positions already, such as multiple pieces on the same square, and a subset of cases where the king of the side not to move is in check.

[h.g.muller]

..., and a subset of cases where the king of the side not to move is in check.

The key here is the word 'subset'. I know how Nalimov treats indexing of the King locations, which would exclude all positions where the side not to move is in check by the opponent King. But this is reciprocal, so it should not cause a difference in the number of wtm and btm broken positions. Are some other 'king-capture' positions also excluded?

[mbourzut]

Nalimov not only excludes positions where the kings are adjacent, but also other "unblockable" checks. For example, a white knight on f6 and black king on g8 with wtm is illegal regardless of where the other pieces are, similar for example a white rook on f8 and a black king on g8. These exclusions are obviously not reciprocal.

[h.g.muller]

OK, that would explain it. Thanks!