Abstract: | Let (Mr)r∈?0 be a logarithmically convex sequence of positive numbers which verifies M0 = 1 as well as Mr ≥ 1 for every r ∈ ? and defines a non quasi - analytic class. Let moreover F be a closed proper subset of ?n. Then for every function f on ?n belonging to the non quasi - analytic (Mr)-class of Beurling type, there is an element g of the same class which is analytic on ?,n F and such that Dαf(x) = Dαg(x) for every α ∈ ?n0 and x ∈ F. |