Black to play: 30 ... ?

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<30 ... Ke5?

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[30...Na3 is the only move to stay afloat. The knight is completely stupid on a3, but it's safe and Black threatens the a-pawn, and that's enough to keep things messy.]

31.Rb2

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Now it's completely over, due to the threat of Nb4/Ne3.>

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The position after 31 ♖b1-b2 is a perfect example of what I call <PINNED + LOOSE = ZUGWANG>.

Because the White b2-rook is on an open line on the 2nd rank, the White b2-rook is threatening ♖b2x♘c2 *and* ♖b2x♖d2. This is the <BALEFUL INFLUENCE> property of line pieces, that they threaten <EVERY SINGLE SQUARE (ESS)> on their lines.

To meet the threat of ♖b2x♘c2, Black is <DEFENDING> the c2-knight,square with his Black d2-rook from the only square d2. So if the Black d2-rook moves, it puts the c2-knight <EN PRISE>.

And likewise, to meet the threat of ♖b2x♖d2, Black is <BLOCKING> the line from b2 to d2 @ c2, again from the only square. So if the Black c2-knight moves, it puts the Black d2-rook <EN PRISE>, as the line b2-d2 will no longer be <BLOCKED> at c2.

*So* if the Black c2-knight cannot move because it is <PINNED>, and the Black d2-rook cannot move because it must <DEFEND> the c2-square, <<<neither the Black c2-knight nor the Black d2-rook can move!>>>.

"Magnus played Ivanchuk in round 29 and could still theoretically catch the leaders. He made a mistake in the opening and had to give a pawn on d6 for some activity. <With a rook on d2 and knight on c2 he later equalised but then blundered, allowing Rb2! creating a bind on the black pieces.> Magnus had to sack an exchange and lost quickly">