Some Examples of Hypoelliptic Partial Differential Equations. A. Menikoff — 1976 Mathematische Annalen
Hypoelliptic operators with double characteristics A. Menikoff Séminaire Équations aux dérivées partielles (Polytechnique)
On hypoelliptic operators with double characteristics A. Menikoff — 1977 Annali della Scuola Normale Superiore di Pisa - Classe di Scienze
On the Eigenvalue of a Class of Hypoelliptic Operators. A. Menikoff; J. Sjöstrand — 1978 Mathematische Annalen
The eigenvalues of hypoelliptic operators A. Menikoff; Johannes Sjöstrand — 1977 Journées équations aux dérivées partielles