Suppose that g$g$ is a complex semisimplesemi-simple Lie algebra and g'$g'$ its reductive subalgebra.
If \tau$\tau$ is an involutive automorphism of g'$g'$, can \tau$\tau$ be extended to an involutive automorphism of g$g$ in general?
If not in general, for what kind of pair (g, g')$(g, g')$ or \tau$\tau$, this is true?