  Let $F$ be an arbitrary field and let $f:V\times V\to F$ be a non-degenerate
symmetric or alternating bilinear form defined on an $F$-vector space of finite
dimension $m\geq 2$. Let $L(f)$ be the subalgebra of $gl(V)$ formed by all
skew-adjoint endomorphisms with respect to $f$. We find a composition series
for the $L(f)$-module $gl(V)$ and furnish multiple identifications for all its
composition factors.
