Radical and socle series of a direct sum
= Radical and socle series of a direct sum
For finite-length modules $U,V$ and every nonnegative integer $i$,
$$
J^i(U\oplus V)=J^i(U)\oplus J^i(V),
\qquad
\operatorname{Soc}^i(U\oplus V)=\operatorname{Soc}^i(U)\oplus\operatorname{Soc}^i(V).
$$