On quasi-categories as a foundation for higher algebraic stacks

We develop the basic theory of quasi-categories (a.k.a. weak Kan complexes or ([infinity], 1)- categories as in [BV73], [Joy], [Lur06]) from first principles, i.e. without reference to model categories or other ideas from algebraic topology. Starting from the definition of a quasi-category as a simplicial set satisfying the inner horn-filling condition, we define and prove various properties of quasi-categories which are direct generalizations of categorical analogues. In particular, we look at functor quasi-categories, Hom-spaces, isomorphisms, equivalences between quasi-categories, and limits. In doing so, we employ exclusively combinatorial methods, as well as adapting an idea of Makkai's ("very subjective morphisms," what turn out in this case to be simply trivial Kan fibrations) to get a handle on various notions of equivalence. We then begin to discuss a new approach to the theory of left (or right) fibrations, wherein the quasi-category of all left fibrations over a given base S is described simply as the large simplicial set whose n-simplices consist of all left fibrations over S x [delta]n.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mathematics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Nichols-Barrer, Joshua Paul

Advisor dc:contributor.advisor

• Aisc Johan de Jong.

• Mathematics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/39088

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/39088