Hi everyone, one my textbook there is written (if two system blocks are asintotically stable and are in series, their product will be asintotically stable), but I've heard that sometimes the transfer function of the controller could be not asintotically stable in some cases (see p.i.p. condition), so my question is, since the transfer function of the controller and the transfer function ofmy system are in series, my question is, their product in series will not be asintotycally stable hence my total system won't be stable ?? How does it works for a instable transfer function of my controller ?? And in which cases should i use it ?