1. Bergamasco, A.P., Cordaro, P.D., Malagutti, P.A.: Globally hypoelliptic systems of vector fields. J. Funct. Anal. 114(2), 267–285 (1993)
2. Bergamasco, A.P., Dattori da Silva, P.L., Gonzalez, R.B., Kirilov, A.: Global solvability and global hypoellipticity for a class of complex vector fields on the 3-torus. J. Pseudo-Differential Oper. Appl. 6(3), 341—360 (2015)
3. Bott, R.: The index theorem for homogeneous differential operators. In: Differential Combinatorial Topology. A Symposium in Honour of Marston Morse, pp. 167–186 (1965)
4. Cardona, D., Ruzhansky, M.: Subelliptic pseudo-differential operators and Fourier integral operators on compact Lie groups. MSJ Mem., (2024), to appear, Mathematical Society of Japan, Tokyo, 180 Pages. arXiv:2008.09651
5. Cardona, D., Kumar, V. Ruzhansky, M.: Subelliptic Pseudo-Differential Operators on Homogeneous Vector Bundles over Compact Homogeneous Manifolds, (2024), preprint.