“…Local and global G s , 1 ≤ s ≤ ∞, hypoellipticity has been studied by many authors, including Albanese, Corli, and Rodino [1], Amano [3], Baouendi and Goulaouic [4], Bell and Mohammed [5], Bergamasco, Cordaro, and Malagutti [6], Bove and Tartakoff [8], [9], Christ [12]- [14], Cordaro and Himonas [15], [16], Dickinson, Gramchev, and Yoshino [17], Fedii [18], Fujiwara and Omori [19], Gramchev,Popivanov,and Yoshino [20]- [22], Greenfield and Wallach [24], Hanges and Himonas [25], [26], Helffer [27], Himonas [28], [29], Himonas and Petronilho [30]- [33], Himonas, Petronilho, and dos Santos [34], Hörmander [35], [36], Kohn [38], Pham The Lai and Robert [39], Metivier [40], Oleinik and Radkevic [41], Omori and Kobayashi [42], Rodino [47], Rothschild and Stein [48], Tartakoff [49].…”