Resumen de Higher-order tangents and Fefferman's paper on Whitney's extension problem

Wieslawa Pawlucki, Edward Bierstone, Pierre D. Milman

• Whitney [W2] proved that a function defined on a closed subset of R is the restriction of a Cm function if the limiting values of all mth divided differences form a continuous function. We show that Fefferman¿s solution of Whitney¿s problem for Rn [F, Th. 1] is equivalent to a variant of our conjecture in [BMP2] giving a criterion for Cm extension in terms of iterated limits of finite differences.