M. Fliess et H. Mounier, SOME STRUCTURAL-PROPERTIES OF LINEAR-SYST EMS WITH CONSTANT DELAYS, Comptes rendus de l'Academie des sciences. Serie 1, Mathematique, 319(3), 1994, pp. 289-294
Controllability, observability and realization of linear systems with
delays receive a definition in a module theoretic framework. The chang
e of the ground ring as well as the affirmative answer to Serre's conj
ecture permit to understand the connections with most of other widely
used notions.