We classify the Klein
four-subgroups Γ of Aut(u0) for each compact simple Lie algebra u0 up to
conjugation, by calculating the symmetric subgroups Aut(u0)𝜃 and their involution
classes. This leads to a new approach to the classification of semisimple symmetric
pairs and ℤ2× ℤ2-symmetric spaces. We also determine the fixed point subgroups
Aut(u0)Γ.
Keywords
automorphism group, involution, symmetric subgroup, Klein
four-group, involution type