Computation of maximal reachability submodules

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.