Solution
= Solution
For the left regular module, the <radical series of a module> is obtained by multiplying by powers of the <Jacobson radical>:
$$
J^i({}_AA)=J(A)^i=N^i.
$$
Products of <matrix units> show that
$$
\boxed{N^i=\operatorname{span}_k\{e_{rs}:r-s\geq i\},
\qquad0\leq i\leq n,}
$$
with $N^0=A$ and $N^n=0$. Thus each step removes one subdiagonal, and the <Loewy length> of ${}_AA$ is $n$.