1. K. Baba, Local orbit types of the isotropy representations for semisimple pseudo-Riemannian symmetric spaces, Diff. Geom. Appl. 38 (2015), 124–150.
2. M. Berger, Les espaces symétriques noncompacts, Ann. Sci. École Norm. Sup. (3) 74 (1957), 85–177.
3. P. Bravi, G. Pezzini, The spherical systems of the wonderful reductive subgroups, J. Lie Theory 25 (2015), 105–123.
4. M. Brion, Classification des espaces homogénes sphériques, Compositio Math. 63(1987), no. 2, 189–208.
5. P. Delorme, B. Krötz, S. Souaifi, The constant term of tempered functions on a real spherical space, arXiv:1702.04678v1 (2017).