Bulletin of the American Mathematical Society · 1972 · 92 citations · 1 references
We give here an example, as simple as possible, of a degenerate elliptic operator Yj= 1 Xj where X i9 X 2 ,..., X r are r vector fields with analytic coefficients which, with their commutators of order 1, span the whole space, and such that there exists a nonanalytic function u in the Gevrey class G 2 with 5= x X)u = 0.
1