In this paper, we consider the decomposition of a quadratic Lie algebra and
the main result is that the decomposition of a quadratic Lie algebra into
irreducible nondegenerate ideals is unique up to an isometry (Theorem 3.1).
As a corollary, we obtain the uniqueness of the decomposition of an arbitr
ary Lie algebra into indecomposable ideals up to an isomorphism (Corollary
3.5.4).