References
- Chow WL. Über Systeme von linearen partiellen Differentialgleichungen erster Ordnung. Math Ann. 1939;117(1):98–105.
- Agrachev A, Boscain U, Gauthier J-P. The intrinsic hypoelliptic Laplacian and its heat kernel on unimodular Lie groups. J Funct Anal. 2009;256:2612–2655.
- Barilari D, Rizzi L. A formula for Popp’s volume in sub-Riemannian geometry. Anal Geom Metr Spaces. 2013;1:42–57.
- Montgomery R. A tour of subriemannian geometries, their geodesics and applications. Mathematical surveys and monographs. Vol. 91. Providence (RI): American Mathematical Society; 2002.
- Gordina M, Laetsch T. Sub-Laplacians on sub-Riemannian manifolds. Potential Anal. 2016;44:811–837.
- Bauer W, Furutani K. Spectral analysis and geometry of a sub-Riemannian structure on S3 and S7. J Geom Phys. 2008;58(12):1693–1738.
- Chang DC, Li SY. A zeta function associated to the sub-Laplacian on the unit sphere in ℂn. J D’Anal Math. 2002;86:25–48.
- Gromoll D, Meyer W. An exotic sphere with non-negative sectional curvature. Ann Math. 1974;100(2):401–406.
- Hörmander L. Hypo-elliptic second order differential equations. Acta Math. 1967;119:147–171.
- Strichartz RS. Sub-Riemannian geometry. J Differ Geom. 1986;24(2):221–263.
- Sasaki S, Hsu C-J. On a property of Brieskorn manifolds. Tohoku Math J. 1976;28:67–78.
- Vaisman I. On the Sasaki-Hsu contact structure on the Brieskorn manifolds. Tohoku Math J. 1978;30:553–560.