[Boards: 3 / a / aco / adv / an / asp / b / biz / c / cgl / ck / cm / co / d / diy / e / fa / fit / g / gd / gif / h / hc / his / hm / hr / i / ic / int / jp / k / lgbt / lit / m / mlp / mu / n / news / o / out / p / po / pol / qa / r / r9k / s / s4s / sci / soc / sp / t / tg / toy / trash / trv / tv / u / v / vg / vp / vr / w / wg / wsg / wsr / x / y ] [Home]
4chanarchives logo
Compact Sets
Images are sometimes not shown due to bandwidth/network limitations. Refreshing the page usually helps.

You are currently reading a thread in /sci/ - Science & Math

Thread replies: 15
Thread images: 1
File: Fourth_Impact.png (2 MB, 1920x814) Image search: [Google]
Fourth_Impact.png
2 MB, 1920x814
SOUP /SCI/ what was your definition of compactness? / define a compact set in your own words; feel free to define other terms as you please.

Example:
Definition: A set [math]E[/math] is [math]compact[/math] iff, for every family of sets [math]{G_α}_(α \in A)[/math] of *open* sets such that [math]E \subset \bigcap_(α \in A)G_α[/math], there is a finite set [math] {α_1, ..., α_n} \subset A[/math] such that [math]E /subset (/bigcup^n)_(i=1)G_α[/math]
>>
A point is connected to a point if there is a path (obviously continuous) that connects them.
A connected set is a set where every point in it is connected to all other points of the set.
Inuitive and a rigorous definition in almost all contexts
>>
A set [math]S[/math] is compact if and only if every sequence [math]s:\mathbb{N}\to S[/math] has a subsequential limit in [math] S[/math]
>>7973281
I think I like this the path-connected definition of connectedness the most
>>
Any open cover has a finite subcover.

>>7973291
Sequential compactness (the definition you gave) isn't equivalent to compactness in general topological spaces (only in metric spaces).
>>
>>7973311
Metric topology = best topology
>>
>>7973281
Path connectedness isn't the same thing as connectedness, not even in metric spaces. The topologist's sine curve is the standard example of a connected but not path connected space. A topological space is connected if the only clopen subsets are the empty set and the whole space.
>>
>>7973313
Zariski topology is best topology. Hausdorff spaces are for losers.
>>
>>7973320
regular locales are the best
>>
>>7973320
I never understood the fascination with primes (sorry I'm not far enough in math to really understand a prime ideal or w/e)
>>
>>7973330
I've done that and it still isn't that interesting
>>
>>7973242
Fix your fucking LaTeX.

>>7973311
This. Open cover compactness is best compactness.

>>7973330
It's basically autism.
>>
is there a way to study topology without resorting to imaginary things like infinite sets?
>>
>>7974286
I'm pretty sure there is intuitionistic topology.
>>
>>7973330
The Nullstellensatz give a correspondence between points in [math]\mathbb C^n[/math] and maximal ideals of [math]\mathbb C[x_1,\dotsc,x_n][/math]. Interesting things happen if you extend this to prime ideals.
>>
>>7974286
predicative locale theory ?
Thread replies: 15
Thread images: 1

banner
banner
[Boards: 3 / a / aco / adv / an / asp / b / biz / c / cgl / ck / cm / co / d / diy / e / fa / fit / g / gd / gif / h / hc / his / hm / hr / i / ic / int / jp / k / lgbt / lit / m / mlp / mu / n / news / o / out / p / po / pol / qa / r / r9k / s / s4s / sci / soc / sp / t / tg / toy / trash / trv / tv / u / v / vg / vp / vr / w / wg / wsg / wsr / x / y] [Home]

All trademarks and copyrights on this page are owned by their respective parties. Images uploaded are the responsibility of the Poster. Comments are owned by the Poster.
If a post contains personal/copyrighted/illegal content you can contact me at [email protected] with that post and thread number and it will be removed as soon as possible.
DMCA Content Takedown via dmca.com
All images are hosted on imgur.com, send takedown notices to them.
This is a 4chan archive - all of the content originated from them. If you need IP information for a Poster - you need to contact them. This website shows only archived content.