“…Under these assumptions, the operator T, in essence, is a set of integrodifferential equations relating the output to the input and an auxiliary equation that satisfies the initial conditions. In system theory, the procedure of associating a number of independent variables together is called association of variables [5]. If it is possible to associate t and s in the t; s ð Þ-domain, the system operator T can be considered to be a Volterra functional operator [6], which, in general, represents a nonlinear dynamic system.…”