On homotopy varieties

Given an algebraic theory \ct, a homotopy \ct-algebra is a simplicial set where all equations from \ct hold up to homotopy. All homotopy \ct-algebras form a homotopy variety. We give a characterization of homotopy varieties analogous to the characterization of varieties. We will also study homotopy models of limit theories which leads to homotopy locally presentable categories. These were recently considered by Simpson, Lurie, To\"{e}n and Vezzosi.Comment: Proposition 4.5 is not valid; see Remark 4.5(e) in the new version. All other results are correct but there are gaps in proofs. They are fixed by reducing simplicial categories to fibrant ones and replacing homotopy colimits by fibrant ones, as wel

Are all cofibrantly generated model categories combinatorial?

G. Raptis has recently proved that, assuming Vop\v{e}nka's principle, every cofibrantly generated model category is Quillen equivalent to a combinatorial one. His result remains true for a slightly more general concept of a cofibrantly generated model category. We show that Vop\v{e}nka's principle is equivalent to this claim. The set-theoretical status of the original Raptis' result is open

Homotopy locally presentable enriched categories

We develop a homotopy theory of categories enriched in a monoidal model category V. In particular, we deal with homotopy weighted limits and colimits, and homotopy local presentability. The main result, which was known for simplicially-enriched categories, links homotopy locally presentable V-categories with combinatorial model V-categories, in the case where has all objects of V are cofibrant.Comment: 48 pages. Significant changes in v2, especially in the last sectio