Suggestion: Forced draw gets marked in engine evaluation

When analyzing a game, a position can be equal but playable or a forced draw by repetition/perpetual check. Both get evaluated as 0.0 but marking these two types of equality differently would give some useful additional insight. Maybe the forced draw could show "0.0 (D)" in the evaluation.

I would define a "forced draw" where the best continuation is only to allow a repetition of moves. For example, allow a perpetual otherwise get mated would be considered a force draw. But allow a perpetual or continue an equal position is not a forced draw. I'm sure the definition could be refined, but at least that's my intuition.

That would also leave the door open for other types of equality classifications like table-base, insufficient material, or no legal mating construction.

But I'm most interested in the forced draw because a winning position can suddenly go to 0.0 because a mistake lets the opponent find a tricky line that forces the draw.

This is really something the chess engine itself would have to support, rather than lichess. As far as I'm aware, stockfish doesn't currently support this feature (and I'm not aware of any major engine that does).

The closest you could do is look at the PV (the principal variation, or the moves that the engine is suggesting) to see if it ends in a threefold draw, but that's not really proof at all - there may be other move choices, equally or nearly equally precise, that play on, and the engine wouldn't supply those.

It does seem a good idea...especially with the confusion that can arise from three-reps.

@qqskew said in #4:
> Nonetheless, I think it would a useful tool - perhaps someone can build
I'm sympathetic, but what do you suggest they do? Build a modified version of Stockfish that has a different evaluation method, and then make it available as an external engine? Something else?

Good idea, but there would be a lot to define.
-> Is it "forced draw" if you can choose between 50st reversible move or a pawn move?
-> Is it "forced draw" if you can get the same position the third time or decide for an alternate move?
-> Is it "forced draw" if you could stalemate your opponent even if your position is better?
But I am sure there is a solution.