T Ganea,
Lusternik-Schnirelmann category and strong category,
Illinois J. Math. 11 (1967) 417–427 MR0229240
2
S Helgason,
Differential geometry, Lie groups, and symmetric spaces,
Graduate Studies in Mathematics 34, American Mathematical
Society (2001) MR1834454
Corrected reprint of the 1978 original
M Mimura, H
Toda, Topology of Lie groups. I, II, Translations of
Mathematical Monographs 91, Amer. Math. Soc. (1991) MR1122592
Translated from the 1978 Japanese edition by the authors