Th\'eories homotopiques des 2-cat\'egories

This text develops a homotopy theory of 2-categories analogous to Grothendieck's homotopy theory of categories developed in "Pursuing Stacks". We define the notion of "basic localizer of 2-Cat", 2-categorical generalization of Grothendieck's notion of basic localizer, and we show that the homotopy theories of $Cat$ and 2-$Cat$ are equivalent in a remarkably strong sense: there is an isomorphism, compatible with localization, between the ordered classes of basic localizers of $Cat$ and 2-$Cat$. It follows that weak homotopy equivalences in 2-$Cat$ can be characterised in an internal way, without mentioning topological spaces or simplicial sets.
Comment: in French. Previously contained an appendix by Dimitri Ara which has been separately published as arXiv:1607.03644. Ara proves the existence, for almost every basic localizer W of 2-Cat, of an associated "Thomason model structure" on 2-Cat. He shows that these model category structures model exactly combinatorial left Bousfield localizations of the classical homotopy theory of simplicial sets