Minimal Microlocal Gevrey Regularity for “Sums of Squares”

A theorem of minimal microlocal Gevrey regularity is proved for operators that are sums of squares of vector fields with real analytic coefficients, thus providing a microlocal version of a well-known theorem of Derridj and Zuily (“Régularité analytique et Gevrey d'opérateurs elliptiques dégénérés,” Journal de Mathématiques Pures et Appliquées 52 (1973): 65–80).