In game 6 of the World Championship 2021 between Magnus Carlsen and Ian Nepomniachtchi, before Qe6 the engine says +0.9 at around depth 30/99, but I heard supposedly it's a (theoretical) draw. I know there are some cases of fortresses that have evaluations with absolute value greater than 3.0, but this doesn't quite look like a fortress to me.
Is it really a draw?
Is/Are there another term/other terms for this position, assuming it's a draw?
[FEN "4k3/8/8/4PR2/5P2/6NK/q7/8 b - - 0 1"]
Summary. There is no question. It is a theoretical draw (see tablebase).[1]
Obviously to mere mortals, playing on may hold practical chances for one side. GM Nakamura repeatedly said that the positions in Game 6 of the WCC were extremely difficult to play for Black.
Details. In this position, Black only has two moves that draw: ...Qb1 and ...Qc2 (without considering the 50 move rule).
As pointed out by @Glorfindel, perfect play after multiple Black moves would lead to win by White, but after the 50 move rule would have been invoked. With that considered, in the diagrammed position Black can play: ...Qa1, ...Qa7, ...Qa8, ...Qd2, ...Qd5, ...Qf2, ...Qa3, ...Qa4, ...Qb3, and yes, even Qe6, provided that Black continues to play perfectly.
Regarding the practical side, GM Hikaru Nakamura repeated said that many of the theoretically drawn positions in Game 6 of the 2021 World Chess Championship game were extremely difficult to play as Black. Other super GMs also said many lines in the tablebases had successively fewer and fewer move options for Black to maintain the draw. As a human, this means the right move(s) may become almost impossible to find as the ideas become more difficult to spot.
[1] For positions with 7 or less pieces in total on the board (from both sides), the theoretical status is known. All legal moves have been explored with the outcomes recorded. Read more on endgame tablebases here.
Edit: The OP has asked if this position is a fortress.
Fortresses are often defined by multiple properties:
- Useful pawn breakthroughs are not possible.
- If the stronger side has pawns, they are firmly blocked.
- The stronger side's king cannot penetrate, either because it is cut off or near the edge of the board.
- Zugzwang positions cannot be forced, because the defender has waiting moves available.
Clearly the tablebase shows there is a way for Black to hold indefinitely. Whether that meets the fortress definition, I do not know.
Playing through multiple tablebase lines shows that White can maneuver to use King or Pawn moves to put Black into only move situations. From a practical (human) perspective, that seems pretty useful so maybe this isn't a fortress. If you are a computer playing Black, you aren't scared of such things (so maybe it is).
The other answers have answered the first question. For the second, these positions where one person is winning but is foiled by the 50-move rule are known as "cursed wins".
