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    • CommentRowNumber1.
    • CommentAuthorMike Shulman
    • CommentTimeJan 27th 2012
    • CommentRowNumber2.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJul 30th 2015

    I added several recent references.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeJul 30th 2015

    I have cross-linked with directed homotopy theory

    • CommentRowNumber4.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJun 18th 2018

    I corrected a Unicode problem in Jiří Rosický’s name.

    Curiously, his name does not redirect to the article Jiří Rosický, even though it is hyperlinked.

    Instead, clicking on the hyperlinks attempts to create a new page with the same name (!).

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeJun 18th 2018

    Thanks for the alert. I have now copy-and-pasted the name from the entry title into the entry. The rendering looks the same, but now the link works, so probably there was some unicode ambiguity at play, or the like. (?) A similar issue still happens with hyphens here and there.

    • CommentRowNumber6.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJun 18th 2018
    • (edited Jun 18th 2018)

    Re #5: I think the nLab does not normalize Unicode characters. As a result, the same letter ř, say, can be encoded in two different ways: as a single code point and as r followed by a combining character.

    I suggest that we add a Unicode normalization step during the CGI processing of submitted forms.

    • CommentRowNumber7.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJan 18th 2020

    Delta-generated spaces are cartesian closed.

    diff, v8, current

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeJun 5th 2020

    I have added (here) statement of the proposition that Delta-generated spaces are the fixed points of the adjunction between topological spaces and diffeological spaces

    diff, v9, current

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeJun 5th 2020

    I have also turned the single previous sentence about categorical properties into the statement of two Propositions with pointers to the references where the proofs are to be found.

    diff, v9, current

    • CommentRowNumber10.
    • CommentAuthorDavid_Corfield
    • CommentTimeJun 6th 2020

    Would it add anything worthwhile to describe Delta-generated spaces as those diffeological spaces for which the unit is an isomorphism?

    • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeJun 6th 2020
    • (edited Jun 6th 2020)

    I have added a remark (here) that Δ\Delta-generated is the same as “Euclidean generated”:


    For each nn the topological simplex Δ n\Delta^n is a retract of the ambient Euclidean space/Cartesian space n\mathbb{R}^n (as a non-empty convex subset of a Euclidean space it is in fact an absolute retract). Hence the identity function on Δ n\Delta^n factors as

    id:Δ top ni n np nΔ top n. id \;\colon\; \Delta^n_{top} \overset{i_n}{\hookrightarrow} \mathbb{R}^n \overset{p_n}{\longrightarrow} \Delta^n_{top} \,.

    It follows that every continuous function ff with domain the topological simplex extends as a continuous function to Euclidean space:

    Δ top m f X i n n \array{ \Delta^m_{top} &\overset{f}{\longrightarrow}& X \\ \mathllap{{}^{i_n}}\big\downarrow & \nearrow _{\mathrlap{\exists}} \\ \mathbb{R}^n }

    Therefore the condition that a topological space XX be Δ\Delta-generated (Def. \ref{DeltaGeneratedSpace}) is equivalent to saying that its topology is final with respect to all continuous functions nX\mathbb{R}^n \to X out of Euclidean/Cartesian spaces.

    We might thus equivalently speak of Euclidean-generated spaces.


    diff, v12, current

    • CommentRowNumber12.
    • CommentAuthorUrs
    • CommentTimeJun 6th 2020

    I have expanded the statement about convenience (here). Currently it reads as follows:


    The category of Δ\Delta-generated spaces (Def. \ref{DeltaGeneratedSpace}) is a convenient category of topological spaces in that:


    diff, v15, current

    • CommentRowNumber13.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJun 6th 2020

    Do we have an example that shows that Δ-generated spaces are not locally cartesian closed?

    The quasitopos of diffeological spaces is locally cartesian closed, and Δ-generated spaces are reflective inside all diffeological spaces. Does this tell us anything about local cartesian closedness of Δ-generated spaces?

    • CommentRowNumber14.
    • CommentAuthorUrs
    • CommentTimeJun 7th 2020

    I have added a remark (here) on the terminology “D-topological space” (as discussed in another thread here)

    diff, v19, current

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