“…Hilbert spaces for the formulation of equilibrium points, stability, controllability [16,18,19], boundedness, and square integrability (or summability in the discrete formalism) of the solution in the framework of square-integrable (or squaresummable) control and output functions are of relevant importance in signal processing and control theory and in general formulations of dynamic systems, in general. See, for instance, [1,2,7,9,16,17,19,20] and the references therein. Two examples with the use of the above formalism to dynamic systems and control issues are now discussed in detail.…”