Columbia subject headings:
Differential equations, Hypoelliptic.
Lie groups.
Microlocal analysis.
Pseudodifferential operators.
Harvard subject headings:
Differential equations, Hypoelliptic.
Lie groups.
Microlocal analysis.
Pseudodifferential operators.
Princeton subject headings:
Differential equations, Hypoelliptic.
Lie groups.
Pseudodifferential operators.