  A new and conceptually simple procedure is derived for the compu- tation of
the maximal reachability submodule of a given submodule of the state space of a
linear discrete time system over a Noethenian ring R. The procedure is
effective if R is effective and if kernels and inter- sections can be computed.
The procedure is compared with a rather different procedure by Assan e.a.
published recently.
