this post was submitted on 19 Apr 2025
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submitted 4 days ago* (last edited 3 days ago) by vatlark@lemmy.world to c/til@lemmy.ca
 

The theorem has been expressed colloquially as "you can't comb a hairy ball flat without creating a cowlick" or "you can't comb the hair on a coconut".

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[–] grrgyle@slrpnk.net 47 points 4 days ago (2 children)

A hairy doughnut … on the other hand, is quite easily combable.

What gives someone the right to speak like this. You think this is the kind of factoid I can just forget?? No, this meme is going to jockey my brain until the day I die.

[–] critical@reddthat.com 6 points 3 days ago (1 children)
[–] Kolanaki@pawb.social 6 points 3 days ago (1 children)

"CHICKEN JOCKEY!"

throws popcorn at phone screen

[–] grrgyle@slrpnk.net 3 points 3 days ago (1 children)

My nephews have been screaming this. I thought they were just insane, but apparently I've missed a meme!

[–] can@sh.itjust.works 2 points 3 days ago
[–] TonyTonyChopper@mander.xyz 4 points 3 days ago

I want to know more. Does this only work for donuts with 1 hole? Odd numbers of holes?

[–] Trainguyrom@reddthat.com 4 points 2 days ago

I remember first hearing about the Hairy Ball Theorum when watching some of the extended features on our Monster's Inc DVD. One of the animators was talking about how they had to constantly be re-combing Sully's hair to make sure the cowlick was in an unseen location

I'll have to poke around at some point because there was a really neat video on that DVD as well that was talking about the origin of the Monsters Inc universe, and how the monsters both discovered the power of screams and built the doors/portals for reaching the human world and I remember it being super interesting and extremely fleshed out for something that literally never happen on screen and probably doesn't influence anything on-screen at all

[–] untakenusername@sh.itjust.works 3 points 2 days ago (1 children)
[–] stevedice@sh.itjust.works 2 points 2 days ago
[–] isVeryLoud@lemmy.ca 18 points 3 days ago (1 children)
[–] GreyEyedGhost@lemmy.ca 3 points 3 days ago (1 children)

And where is the cowlick on there...

[–] funkless_eck@sh.itjust.works 7 points 3 days ago (1 children)

buy it dinner and wherever you want

[–] isVeryLoud@lemmy.ca 1 points 2 days ago* (last edited 2 days ago)

With three extra stomachs, that'll cost ya!

[–] pheerai@discuss.tchncs.de 5 points 3 days ago (1 children)

For mathematicians in Germany, this is known as the "Hedgehog Theorem" ("Satz vom Igel", as in "you can't fully comb a hedgehog")

[–] vatlark@lemmy.world 3 points 2 days ago

I think it would be hard to find a hedgehog that would allow itself to be combed.

[–] Maalus@lemmy.world 1 points 2 days ago

By moving the entire comb parallel, sure. But you can move one end slower than the other (i.e. as if you planted one end and pivoted it around, just with some speed, not stationary) and you can comb it without it.

[–] vaguerant@fedia.io 21 points 4 days ago (2 children)
[–] vatlark@lemmy.world 3 points 3 days ago (1 children)

Thanks, I expected it would figure itself out. But I guess it only works in the desktop -> mobile direction, not the reverse.

[–] vaguerant@fedia.io 1 points 3 days ago

Totally, I don't understand why it doesn't work that way.

[–] muntedcrocodile@lemm.ee 4 points 4 days ago (1 children)

Why does Wikipedia do this?

[–] ltxrtquq@lemmy.ml 11 points 4 days ago (1 children)

Whoever posted the link was on mobile at the time and didn't feel like deleting the m. after copy pasting.

[–] muntedcrocodile@lemm.ee 9 points 4 days ago (1 children)

Yeah ik. Just confused why Wikipedia itself does it

[–] jagged_circle@feddit.nl 7 points 4 days ago (2 children)

Does what? Have a separate site for mobile viewing? There's many good reasons..

[–] muntedcrocodile@lemm.ee 9 points 4 days ago (1 children)
[–] jagged_circle@feddit.nl 4 points 3 days ago (2 children)

How else do you do it? Cookies? JavaScript? That would be terrible.

[–] FooBarrington@lemmy.world 9 points 3 days ago

Responsive design usually doesn't require detecting anything about the client. There's probably some differences in actual HTML markup between mobile/non-mobile Wikipedia, but I'd be surprised if it has to be that way. Media queries have been available for a long, long time.

[–] muntedcrocodile@lemm.ee -2 points 3 days ago* (last edited 3 days ago) (1 children)

read the user agent when u visit the link like every other site ever

[–] jagged_circle@feddit.nl 3 points 3 days ago

Shitty sites with stupid devs*

[–] nogooduser@lemmy.world 5 points 4 days ago (2 children)

It would be better to handle it by detecting what device you’re on rather than having encoded into the url. That way it wouldn’t matter what device the page was shared from.

[–] sga 4 points 4 days ago* (last edited 3 days ago) (2 children)

usually it is just a redirection. One of the reasons wiki does this is that their stack is more older device friendly (for the most part, you can use wikipedia perfectly fine without any js), and having adaptive view usually requires js (there are some other ways too), but wiki is constrained. So when browser recieves a request from a mobile user agent, they just redirect to mobile site.

[–] FooBarrington@lemmy.world 5 points 3 days ago (1 children)

Responsive design usually doesn't need JS, it's mostly pure CSS.

[–] sga 0 points 3 days ago (1 children)

That may be the case, but i have seen websites use js for it. Another thing is, what version of css does wikipedia target, as ye older verisons might not have that.

[–] FooBarrington@lemmy.world 3 points 3 days ago (1 children)

Sure, some websites do that, but it's simply wrong to say "having adaptive view usually requires js". No, it doesn't, usually responsive design doesn't need JS.

If a browser doesn't support media queries, it would just show the desktop version. Media queries have been broadly supported since 2015. It's possible that Wikipedia still targets older browsers, but IMO it would be fine to show the desktop version on mobile browsers older than that.

[–] sga 0 points 3 days ago (1 children)

Even in my original comment i said there are non js ways. But what i primarly meant here is, there are differnt "ideas" of implementing a mobile site, some just change element sizes, and make them vertical viewing friendly, but others do change quite a lot, for example, remove most clickable items from the header-bar or title bar, and move them to a kebab/hamburger menu. And I know even this particular example can be done in pure css, but I still feel my statement is not simply wrong.

Also I am not a front end dev, so I am sorry if I get stuff wrong.

[–] FooBarrington@lemmy.world 2 points 3 days ago

No, you're right. The important part I wanted to highlight is that the usual way is CSS, not JS. There are a bunch of websites that use JS for this purpose, and probably also many CMSs etc., but doing it using CSS is far more common.

[–] jagged_circle@feddit.nl 3 points 3 days ago (1 children)

Its not just old devices. I turn js off for security. There's a whole class of high-risk users that this is for. Even on modern hardware and software.

[–] sga 1 points 3 days ago* (last edited 3 days ago)

me too, i was simplifying it. I have a global js disable rule, and whitelist a shorter list

[–] jagged_circle@feddit.nl 1 points 3 days ago* (last edited 3 days ago) (1 children)

That's a terrible idea. Because many users change their user agent for security.

No, you can't expect to detect what devices someone has. That's the thought process of an inexperienced dev.

[–] nogooduser@lemmy.world 0 points 3 days ago (1 children)

They already do this to redirect from the desktop view to the mobile view so they could do it the other way but don’t for some reason.

If a user changes their user agent to something that would cause a site to not be able to determine whether they are on desktop or mobile then they can expect that some sites aren’t going to work well.

[–] jagged_circle@feddit.nl 3 points 3 days ago (1 children)

The problem is that the site tries to detect the device type. If you let the user choose it and make it sticky by domain, you dont have that issue.

[–] nogooduser@lemmy.world 0 points 3 days ago (1 children)

But your users have the problem that they go to the wrong site if someone on a mobile device shares a link when you’re on desktop.

It just seems inconsistent for them to detect mobile devices but not desktop devices.

[–] jagged_circle@feddit.nl 1 points 3 days ago

That doesn't sound like a problem. It sounds like a feature.

[–] icerunner_origin@startrek.website 7 points 4 days ago (1 children)

Shave 'em. I don't want no cowlick near my balls

[–] LiterallyLMAO@lemmy.world 7 points 3 days ago (1 children)

You haven't lived until a cow licks your balls.

[–] anotherandrew@lemmy.mixdown.ca 3 points 3 days ago (1 children)

I guess the closest I've gotten to that is to have a cow lick the "T" off of the "Passat" lettering on my trunk a couple years ago.

[–] GreyEyedGhost@lemmy.ca 1 points 3 days ago (1 children)

...where were your balls when that happened?

nowhere near the trunk of the car, thankfully. :-)