## Subtitles section Play video

• Alright, we're gonna do some street maths

• here in the outdoors,

• which I've heard a lot about.

• But first...

• my shoe is untied.

• So we need to fix that.

• Now, most people would mess around doing some kind of complicated knot,

• not me - I'm a mathematician.

• I've got maths to do.

• Grab the two sides, pass 'em over, boom! There's your knot.

• Again, in slo-mo!

• I'd heard about it, you know, on the maths circuit.

• People would discuss the way that you tie your shoes, right?

• And so – I know it's been around for a long time, I know it's been passed down

• from mathematician to mathematician.

• But I'm not familiar with the earliest case, and I have heard names assigned to it,

• but I've not come across any one that particularly sticks.

• I just call it "that brilliant way to tie your shoes."

• (Brady) Be honest with me, is that how you do your shoes?

• I do genuinely tie my shoes that way

• I know I'm always talking about it

• I literally tie my shoes that way.

• Up to once a day.

• Once it's done, it looks exactly the same, right?

• So then people won't go, "That's an unusual knot," right?

• But if they actually see it happening

• It's like they've seen a magic trick, right?

• It just blows their mind

• They can't comprehend how a knot can happen so quickly.

• But, I'm not startled; I'm a mathematician!

• I know what I'm doing.

• Okay, you go from completely undone, it starts the same way as a normal knot

• You do your little foundation thing

• Which in maths is called a trefoil

• It has a minimum of three crossings in that particular knot

• Now to tie the actual bow

• You get one shoelace that's coming out the back

• You fold it forward and you hold it on its way down

• So it goes up over the loop and then down

• This one curls back in the opposite direction

• And again you hold it on the way down.

• And then all you do is you take this one on the way down and put it under that loop

• At the same time as taking this one and putting it under that loop

• And then you swap them over to the other hands

• And then you pull them tight, and that is your knot!

• And with a little bit of practice,

• Once you tighten it, hold them on the way down,

• cross, pull, knot.

• So the one that comes out the back, you fold it forward into a loop

• And then you hold it on the way down

• So it goes up and then on the way down you're grasping it

• Same with this one except it goes back

• So it starts at the front, curls back, hold it on the way down

• Now you're gonna take this lace, put it under that loop

• at the same time as taking this lace and putting it under that loop

• So they go past each other

• They swap hands, you pull it tight

• And there's your knot.

• People tie their shoelaces, they get one and they loop the other one around

• and they pull it through, which is the normal way.

• Although I've noticed, of course, Brady wears slip-ons.

• (Brady) Why? What's wrong with them?

• For those of us who have entered adulthood

• We do it a long, complicated way.

• But, the thing is, you end up with a knot that holds your shoe on.

• That's the goal here

• My shoelaces

• Formed with what ordinary people would think is a knot

• Now, nothing of this is a mathematical knot

• Because it has loose ends

• If it has loose ends, you can, in principle, untie it

• And you can form a different knot.

Alright, we're gonna do some street maths

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B1 tie loop mathematician brady lace pull

# Super-fast way to tie Shoelaces - Numberphile

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林宜悉 posted on 2020/03/30
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