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Apr
23
comment What is the suspension used in the Freudenthal suspension theorem?
Does this answer your question or is there something that you'd like me to expand?
Apr
23
answered What is the suspension used in the Freudenthal suspension theorem?
Apr
21
awarded  Popular Question
Apr
21
comment Is there a category of categories?
@user132181 Yes, sort of. See my first answer to the OP.
Apr
20
comment A few identities on differential forms
Have you checked Lee's "Introduction to Smooth Manifolds"? Whatever he proves he does it very thoroughly.
Apr
20
comment Equivalence of definitions for “normal extension” and how to lift isomorphisms to them
@HenrySwanson: You're welcome! I'm happy to hear it was useful. Also, Profs. Clark and Milne have other great sets of notes on their homepages, you might want to check them out.
Apr
20
answered Equivalence of definitions for “normal extension” and how to lift isomorphisms to them
Apr
15
comment Is there a category of categories?
@roman: true enough. I remember "The joy of cats" calling it a "quasicategory", although I don't think I even read how they defined that concept.
Apr
15
accepted When are generalized Severi-Brauer varieties trivial?
Apr
15
answered When are generalized Severi-Brauer varieties trivial?
Apr
15
comment Homology Whitehead theorem for non simply connected spaces
tom Dieck's Algebraic Topology book says (p. 498) that: In (20.1.5) one cannot dispense with the hypothesis that the spaces are simply connected. There exist, e.g., so-called acyclic complexes X with reduced homology groups vanishing but with non-trivial fundamental group. Moreover it is important that the isomorphism is induced by a map. The reference is to your (one version of) Whitehead's theorem. He then goes on to state and prove what you sketched in the comments.
Apr
12
comment Size Issues in Category Theory
@user42912: because the category of small categories is not small.
Apr
12
comment Is there a category of categories?
There is no category of categories, because of size issues. See [this answer][1]. [1]: math.stackexchange.com/a/717993/2614
Apr
10
accepted If a morphism of pushouts of complexes (with one arrow monic) is composed of quasi-isos, then the induced arrow is one also
Apr
6
comment “important” math concepts to pass on to next generation of creatures at some cataclysm
This is more like "how to troll the generation of the future", no?
Apr
5
revised If a morphism of pushouts of complexes (with one arrow monic) is composed of quasi-isos, then the induced arrow is one also
deleted 5 characters in body
Apr
5
comment If a morphism of pushouts of complexes (with one arrow monic) is composed of quasi-isos, then the induced arrow is one also
Yeah, I missed a period at the end of a sentence. Sorry about that :P
Apr
5
answered If a morphism of pushouts of complexes (with one arrow monic) is composed of quasi-isos, then the induced arrow is one also
Apr
2
reviewed Approve suggested edit on Solving a non linear ODE problem
Apr
2
comment Is there an analogue of the universal cover for higher homotopy groups?
This question on MO asks the same question you're asking, I think.