Notes on the differentiation of quasi-convex functions
arXiv:1309.1772
Abstract
This expository paper presents elementary proofs of four basic results concerning derivatives of quasi-convex functions. They are combined into a fifth theorem which is simple to apply and adequate in many cases. Along the way we establish the equivalence of the basic lemmas of Jensen and Slodkowski.
An appendix has been added discussing the Hiriart-Urruty and Plazanet characterization of C^{1,1} in terms of quasi-convexity