“…Qualitative results are related e.g. to stability properties of equilibria and operating points [3,4,5,6,7], oscillations [8,9,10,11], bifurcations [12,13,14] or chaotic phenomena [3,15,16,17,18,19,20,21,22]. These references are just a sample of the huge literature addressing qualitative aspects in electrical and electronic engineering (cf.…”