“…Recently, even large epidemic systems have been successfully treated by Volterra Lyapunov functions, first systems with an arbitrary number of disease stages, both finite [1,17,25,26,46] and distributed [39,42,[47][48][49][50][51], and then systems with an arbitrary, but finite number of subpopulations [13,18,19,35,36], and finally combinations of both [37]. In most of the latter cases, graph-theoretic methods are used (Metzler matrices are used in [13]).…”