[agarden]

Regan's analysis is a good deal more detailed than that. He claims that if you check the computer just three times a game, he is going to catch you within three games. Now, if you check just once, it becomes a lot harder.

For the game against Carlsen, he looked at the key moves in that game. The first 20 or so moves were theory. You can't ever prove cheating in theory. After they diverged from theory, Regan said there were only two really key moves. For both of those, Niemann did not use the computers top choice. One of them he played a downright inaccurate move that could have cost him a tempo.

I don't know if Niemann cheated or did not, or even what exactly Carlsen suspects, but Regan's analysis seems to me to be strong enough that it counterbalances the known character deficiency of Niemann.

[blub]

If there are several good moves, it seems logical to cheat by not picking the computer’s top choice.

[agarden]

If there are three or four good moves of approximately equal strength in a position, then it just isn't a position where someone at grandmaster level needs to cheat or benefits from doing so. They were going to find one of those moves anyway.

[hrunt]

Is it cheating if you make decisions to purposefully not gain an advantage (ignoring gambling-induced outcomes, like throwing a match)?

"He was cheating! An outside influence was telling him which move to make and he purposefully didn't do it!"

[blub]

Like I said, it depends on the available set of moves. If #1 is +1 and #2 is +0.7, but the cheater wanted to play #5 at -0.5 then that’s an outcome-changing difference.

Chess engines like Hiarcs can show a series of good, ok, questionable and bad moves for each touched piece color-coded on the board for example.