Published online by Cambridge University Press: 20 November 2018
This paper is concerned with the structure of the derivation algebra Der L of the Lie algebra L with split Cartan subalgebra H. The Fitting decomposition
of Der L with respect to ad ad H leads to a decomposition
where
This decomposition is studied in detail in Section 2, where the centralizer of ad L∞ in D0(H) is shown to be
which is Hom(L/L2, Center L) when H is Abelian. When the root-spaces La (a nonzero) are one-dimensional, this leads to the decomposition of Der L as
where T is any maximal torus of D0(H).