Topology Lecture 19: Path-Connectedness

We define path-connected topological spaces and show that many of the properties of connected spaces also hold for path-connectedness. Moreover, we prove that path-connectedness implies connectedness, and see a counterexample to the converse statement.
00:00 Introduction
00:25 Motivation
02:10 Definition: Path
03:42 Definition: Path-Connectedness
04:25 Continuous images preserve path-connectedness
10:11 Unions with common point preserve path-connectedness
18:51 Finite products preserve path-connectedness
24:15 Quotients preserve path-connectedness
26:00 Thm: Path-connectedness implies connectedness
31:56 Examples of path-connected spaces
37:28 A connected space which is not path-connected
This lecture follows Lee's "Introduction to topological manifolds", chapter 4.
A playlist with all the videos in this series can be found here:
• Topology

Пікірлер: 9

  • @braindead3201
    @braindead32013 ай бұрын

    For the final example about the connected set that is not path connected, I was having trouble figuring out the detail in the extra notes about the existence of the minimum value a. I managed to figured out a proof which might help others understand. The claim is that there is a minimum a such that g(a)=(0,y). Notice that any value t which satisfies g(t)=(0,y) equivalently satisfies (fg)(t)=0, where f is the projection function along the first coordinate. Hence the set of such t is exactly the set of zeroes for the composite function fg. We know the projection function is continuous and g is continuous by assumption, so fg is also continuous. An important fact to know is that the zeroes of a continuous real function form a closed set. This set is a subset of [0,1], so it is bounded below. This and the fact that it’s closed implies that the set of zeroes contains its infimum. We take this infimum to be the value of a.

  • @leodu561
    @leodu5612 жыл бұрын

    Great quality as usual. Very much look forward to the discussion on compactness after you're done with locally connectedness!

  • @DjhiseMise
    @DjhiseMise2 жыл бұрын

    These videos are so awesome i really hope this playlist reaches even more interesting topics like homotopy someday 😁

  • @richardchapman1592
    @richardchapman1592Ай бұрын

    Wondering if these morphing spaces are used by orian to track down the power of money counter accumulation on the black markets.

  • @justinswag3403
    @justinswag34032 жыл бұрын

    great video

  • @binamra5521
    @binamra55212 жыл бұрын

    Keep going mate ❤️

  • @mariusfurter

    @mariusfurter

    2 жыл бұрын

    Thanks, I will :)

  • @samwright4033
    @samwright4033 Жыл бұрын

    These are so so so helpful! Do you have a video on group topology?

  • @mariusfurter

    @mariusfurter

    Жыл бұрын

    Unfortunately, I don't have any videos covering topological groups yet.