1. On positive Rockland operators;Auscher;Coll. Mat.,1994
2. Unitary representations of Lie groups and Gårding's inequality;Bratteli;Proc. Amer. Math. Soc.,1989
3. Lp-regularity of subelliptic operators on Lie groups;Burns;J. Operator Theory,1994
4. Semi-groups of Operators and Approximation;Butzer,1967
5. Representations of Nilpotent Lie Groups and Their Applications. Part 1: Basic Theory and Examples;Corwin,1990