1. [1] D. V. Alekseevsky and V. Cortés, Isometry groups of homogeneous quaternionic Kähler manifolds, J. Geom. Anal. 9 (1999), 513–545.
2. [2] S. Araki, On root systems and an infinitesimal classification of irreducible symmetric spaces, J. Math. Osaka City Univ. 13 (1962), 1–34.
3. [3] A. L. Besse, Einstein Manifolds, Classics Math., Springer, Berlin, 2008.
4. [4] P. Eberlein and M. Jablonski, “Closed orbits of semisimple group actions and the real Hilbert-Mumford function” in New Developments in Lie Theory and Geometry (Cruz Chica, 2007), Contemp. Math. 491, Amer. Math. Soc., Providence, 2009, 283–321.
5. [5] C. Gordon, Riemannian isometry groups containing transitive reductive subgroups, Math. Ann. 248 (1980), 185–192.