A generalized sharp Whitney theorem for jets.
Charles Fefferman (2005)
Revista Matemática Iberoamericana
Similarity:
Suppose that, for each point x in a given subset E ⊂ R, we are given an m-jet f(x) and a convex, symmetric set σ(x) of m-jets at x. We ask whether there exist a function F ∈ C(R) and a finite constant M, such that the m-jet of F at x belongs to f(x) + Mσ(x) for all x ∈ E. We give a necessary and sufficient condition for the existence of such F, M, provided each σ(x) satisfies a condition that we call "Whitnet w-convexity".