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  • There's a myth that Grandmasters can see ten,

  • fifteen,

  • twenty moves ahead.

  • And it's a great myth

  • because I'm a Grandmaster

  • and it makes me look like a super freaking genius.

  • But the truth is,

  • in just the first four moves

  • there are 318 billion ways you could play.

  • Now that would be cool if I could pull that off,

  • but Grandmasters just can't, it's too much.

  • So we use different techniques to be able to look ahead.

  • And some of these techniques include

  • chunking,

  • which means taking a group, a chess position,

  • and seeing what possibilities can come just that group;

  • or pattern recognition,

  • which is just going over a lot of positions

  • that look very similiarly

  • and extrapolating truths from that;

  • the stepping-stone method,

  • which is to take a position,

  • freeze it in your mind,

  • and go from there to guess the next position.

  • But one of my favorites

  • that I love to solve these kind of chess puzzles,

  • is called retrograde analysis.

  • And what you do with retrograde analysis

  • is that in order to look ahead,

  • it pays to look backwards.

  • Now, why is this so useful?

  • Well, in chess, it's a very complicated case.

  • You got all these chess pieces,

  • it's 32 pieces,

  • but after 5 moves, the position starts to evolve a little bit.

  • And the game starts to go on

  • and you see the chess position get a little simpler,

  • and a little bit simpler,

  • and less pieces on the board,

  • until finally,

  • in this case, a game that I played in a tournament in Foxwoods,

  • it gets to something like this.

  • When great players play,

  • it often gets to something like this.

  • You don't see like some easy, early checkmate.

  • Grandmasters see through all that stuff.

  • What you see is some end game,

  • something really, really simple.

  • And we like to study things like this,

  • Grandmasters do,

  • so that if we get to them,

  • we know how to play them cold,

  • but also so that we can steer

  • in the position that's in front of us,

  • the more complex ones you saw earlier,

  • to something this easy,

  • something this simple.

  • So in this way, when you're dead,

  • I already knew like ten moves ago

  • because I knew where we were going.

  • Now, why is this so effective?

  • Well, it's something about the human mind,

  • the problem with the human mind.

  • We're very logical creatures.

  • So I want you to play along with me a few games.

  • Take a look at this sentence.

  • Now most of you reading the sentence

  • the second time around

  • will realize that you missed the word "the"

  • the first time around.

  • Your mind is very logical,

  • it proceeds forward,

  • it just ignores anything that breaks with its logical stream,

  • and so you don't see the word "the" the first time,

  • the second "the," the first time you read it.

  • But if you read this sentence backwards,

  • you would automatically catch it.

  • You'd go backwards,

  • and you get to "brain",

  • and you get to "the,"

  • and then you say, "Whoa, there are two 'the's' in the sentence."

  • This is a really cool trick for proofreading papers.

  • You know, you're writing your paper

  • and there are these silly mistakes.

  • Why are these mistakes in my paper?

  • You read it backwards, you'll catch all of them.

  • Alright, let's go on to this problem, an interesting problem.

  • "Bacteria that double every 24 hours

  • fill a lake it has infested after precisely 60 days.

  • On what day was the lake half-full?"

  • Now, a lot of people had seen this problem

  • and they'd think, "30, like, you know, you split it in half."

  • Well, that's not the right answer.

  • And, also, people might want a calculator.

  • It's too big, it's math, it's boring,

  • I don't want to do that either.

  • But, if you do that problem backwards,

  • you get the answer right away.

  • What's the answer?

  • 59, obviously.

  • You start at the end, you go backwards,

  • it's like, "Oh yeah, it's half-full, the answer is 59."

  • Here's another puzzle, a little bit more complicated.

  • You have six numbers, 1 through 6.

  • The cards are face-down.

  • You and I are going to pick a card.

  • You pick a card and you look at it

  • and it says the number 2.

  • I look at my card,

  • I think about it for a minute

  • and I say, "I want to trade."

  • The reason I want to trade,

  • we're going to trade to see

  • who has the highest number at the end.

  • Do you trade with me?

  • Most people say, "Of course, I got a 2, 2 sucks!

  • There are four numbers higher,

  • probability says I'm going to do better."

  • Wrong answer, you're playing a Grandmaster.

  • You start from the back and you work it out.

  • If I had the number 6, would I offer to trade?

  • Of course not, I'm not dumb.

  • What about the number 5?

  • Probably not either,

  • because you're not going to say yes if you have a 6.

  • Well, if 5 is not going to trade and 6 is not going to trade,

  • 4 is going to be like,

  • "I'm not trading either because 5's and 6's don't trade."

  • So you see what happens as we work backwards.

  • 3 is going to realize 4, 5, and 6 - they don't trade,

  • so the offer is definitely a 1

  • and all of you who said yes,

  • thanks for your money.

  • So, this retrograde analysis is used in different places.

  • It's used to prove intoxications hours after an alleged DUI

  • by Pennsylvania police officers,

  • which is kind of cool.

  • Well, it means don't drink and drive.

  • The use of retro-analysis is used in

  • law,

  • science,

  • medicine,

  • insurance,

  • stock market,

  • politics,

  • career planning.

  • But I find its use to be a more interesting place,

  • maybe one of the most interesting uses is in

  • this movie, which I know a lot of you know,

  • The Curious Case of Benjamin Button,

  • where Brad Pitt plays a guy

  • who's living his life backwards.

  • And what this movie makes me think of

  • is that great quote that,

  • well, that quote you often hear from people who are older,

  • that youth is wasted on the young.

  • Well, if you can see the end game,

  • your youth will not be wasted on you.

  • Thank you very much.

There's a myth that Grandmasters can see ten,

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A2 TED-Ed trade chess position analysis logical

【TED-Ed】Working backward to solve problems - Maurice Ashley

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    Sara Wang posted on 2013/12/13
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