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Comment by glomph | Hacker News Reader

Only tangentially related but hey:

There is an interesting trick that was common for a time and still gets referenced by magicians where even the worst chess player can guarantee that they will win at least half of n chess games where n is any even number. They will also be able to appear to need very little time when they get to each table.

The trick of course is just to play each player against another. The magician acts as a proxy and makes the moves of one player against another. Of course it takes a little practice at memorisation but magicians are often practised at mnemonics anyway.

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This is part of the plot of Sidney Sheldon's If Tomorrow Comes. A woman on a cruise ship with two chess grandmasters bets a large amount of money that she can draw a game with each of them. Of course she plays them at the same time, one game with white, the other black.

It's hilariously improbable to chess players, but some of my non-playing friends thought it was clever.

Lot people do this in online chess games by using a computer.

If you do this too much your ranking gets raised. And at that point, why bother?

Derren Brown pulled this off but with 9 boards, scoring 4W 3L 2D. The strongest players he played "against" each other and was able to beat the weakest (relatively speaking) player there. Quite impressive.

https://www.youtube.com/watch?v=evZmpsl3jI0

I doubt he actually had to "beat" anyone. Magicians don't like to do tricks that might not work :).

> Magicians don't like to do tricks that might not work :)

I actually don't think this is true. As I understand it, a given routine will have a number of high-risk tricks that may work, say, only 1-in-3 times. If they do work, they're highly effective, precisely because they're so implausible, and if they don't work you can just pretend it's a bluff and move onto plan B. It's all about effective showmanship and managing expectations.

(Disclaimer: not a magician!)

That's kind of a cool approach. As long as you can "salvage" the trick, then nobody needs to know about the failed portion.

One of my friends had a card trick that involved me selecting a card. Before starting the trick, he jokingly picked a card at random from the deck, and asked me if that was my card. He had 1/52 chances of being right, but it would have been an insane trick if it had worked.

He guessed wrong (naturally), shrugged and went on with the actual trick as though the first attempt was just a joke, to be forgotten because an actual trick was about to take place.

He may also have been practising a risky method of forcing a card on you. It is standard advice to do this often as it is the only real way of getting good at it.

anyone knows how he did the number predections in the end?

Magic!

Well, it's not always the case but usually a player giving a simul is white in all the games so it's not going to work :)

Unless they manage to lose exactly one move?

Huh? Black and White are not symmetrical, so it's not a matter of chucking a turn somewhere somehow.

They are symmetrical once you mirror.

Nope, it's pretty basic theory that 1 turn advantage changes this symmetry completely. Take a chess board and try it yourself.

That's why you need to lose exactly one move to make it symmetric. Like my original comment said.

And we don't want symmetry on one board, but between two boards.

Still no, you cannot lose a move in the opening. There is no "pass" move in chess. In fact any initial move no matter how wasteful you try to make it, will very soon alter the game. Even rook pawn a3 or h3 will soon have an influence in the game and cannot be ignored. It's very hard to craft the equivalent of a lost move in the early game - say, use an extra move with the bishop or something like that - and it's virtually impossible without the collaboration of the opponent.

Try it yourself vs a few instances of your favourite chess software or just here http://www.chess.com/play/computer (requires Java). Open a few instances and see how can you chuck away a move.

You can't generically just "lose" a move; you can do some three-move wiggles but you'd be relying on your opponent cooperating with you.

Magicians probably wouldn't be playing in the same situations as standard chess players and it would probably be easy to usurp this norm with throw away lines like 'and I don't even need to play as white against all of you'.

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