@article{MZ_1989__201_4_174029,
     author = {Masafumi Yoshino},
     title = {A {Class} of {Globally} {Hypoelliptic} {Operators} on the {Torus.}},
     journal = {Mathematische Zeitschrift},
     pages = {1--12},
     publisher = {mathdoc},
     volume = {201},
     number = {4},
     year = {1989},
     zbl = {0644.35027},
     url = {http://geodesic.mathdoc.fr/item/MZ_1989__201_4_174029/}
}