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Article #114Path connectedness
From: John C. Baez
Date: Mon, 28 Sep 1992 23:36
Date: Mon, 28 Sep 1992 23:36
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I am posting this for Allen Knutson, aknaton@math.Princeton.EDU,
who had trouble posting.
I'm curious about the differences between connectedness and path-connectedness.
If X is a connected topological space with two marked points, say that Y is
X-connected if for all y,y' \in Y one can map in X so as to have X's two
marked points hit y,y' respectively.
Now define a pre-partial order on connected spaces: "X connects more
than X'
does" if being X-connected implies being X'-connected. So for instance, all
R^n's (with whatever two marked points you like) are quickly seen to be
equivalent, but the topologist's sine curve connects strictly more than [0,1]
does.
This partial order (once we mod out by equivalence) plainly has a least
element: spaces where the two marked points coincide. Does it have any
maximal elements? Any canonical choice of representative from a given
connectedness class? Should one restrict to a smaller class of spaces
(say, compact Hausdorff) for some reason? How tall is it? (If people are
bugged by the category of connected spaces not being a set, I'm happy
to just take the ones of cardinality \leq 2^{\aleph_0} or whatever.)
References would be good too. Allen K.
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Newsgroups: sci.math.research Path: arc1-ca.pugleaf.net!sparky!uunet!spool.mu.edu!uwm.edu!ux1.cso.uiuc.edu!news.cso.uiuc.edu!usenet From: "John C. Baez" <jbaez@BOURBAKI.MIT.EDU> Subject: Path connectedness References: <1992Sep28.201204.13907@tamsun.tamu.edu> Nntp-Posting-Host: riesz Message-ID: <1992Sep28.233653.19230@galois.mit.edu> Sender: Daniel Grayson <dan@math.uiuc.edu> X-Submissions-To: sci-math-research@uiuc.edu Organization: MIT Department of Mathematics, Cambridge, MA X-Administrivia-To: sci-math-research-request@uiuc.edu Approved: Daniel Grayson <dan@math.uiuc.edu> Date: Mon, 28 Sep 1992 23:36:53 GMT Lines: 28