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Philippe Gaucher's user avatar
Philippe Gaucher's user avatar
Philippe Gaucher's user avatar
Philippe Gaucher
  • Member for 12 years, 6 months
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Small objects in categories
There are also some facts about $\Delta$-generated spaces not in your references in Section 2 of my paper Homotopical interpretation of globular complex by multipointed d-space.
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L'Intermédiaire des mathématiciens
@FranzLemmermeyer Use a VPN.
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Formalizations of category theory in proof assistants
One suggestion : the proof assistant Mizar works in a variant of ZFC. And its library of certified proofs is already very huge. You could investigate in this direction. Unlike many people, I don't think that coq is appropriate for formalizing math: because the axiom of choice and the law of excluded middle cannot live together in coq. The situation seems to be different with HoTT, as far as I understand the theory.
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Homotopy groups of filtered homotopy limits
I don't understand the last part of your question. What is the translation of your question for the more general setting of a simplicial proper model category ?
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Reference request: colimits of locally presentable categories
@TomLeinster I understand now: with the hipster terminology, a presentable category is not necessarily presentable.
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Reference request: colimits of locally presentable categories
@DylanWilson Me too, I would like to know what could be a globally presentable category.
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Reference request: colimits of locally presentable categories
And also a right adjoint between locally presentable categories is always accessible.
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Reference request: colimits of locally presentable categories
What is a presentable category ? And what is a cocontinuous functor ? I don't understand (i). If you mean a colimit-preserving functor between locally presentable categories, indeed it has a right adjoint by the dual of the Special Adjoint Functor theorem (take the opposite categories and apply SAFT). And an accessible limit-preserving functor between locally presentable categories is always a right adjoint indeed. This is explained in the book you mention.
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Examples of common false beliefs in mathematics
About Computer science: "It is known that quantum computers can solve NP complete problems in polynomial time." A wrong believe is rather that quantum computers can calculate more things than classic computers; which is false. quantum calculability is equivalent to classic calculability.
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About (co)limits of accessible categories
@ZhenLin The meaning of homotopy limit was a part of the question.
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Periods and commas in mathematical writing
I did not use commas and periods in my display-mode formulae until an editor one day added periods and commas almost everywhere before publishing the paper. Now I use them... most of the time. :-).
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Finite simplicial sets
@PeterLeFanuLumsdaine yes indeed.
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Finite simplicial sets
Simpler: $\Delta[n]\subset \Delta[n+1]$ and then consider the colimit of the tower.
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Intuitionistic algebraic topology?
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Yoneda on a not so small category
The trick is to use as many Grothendieck universes as you need : $\mathcal{U_1}\subset \mathcal{U_2}\subset \dots$ and to see where your objects are in this hierarchy of universes. If the final object you are interested in belongs to $\mathcal{U}_1$, you win because it is an ordinary set.