“…Subsystems, witnesses and notions of minimality. Our definition of subsystem is essentially the same to the definition in [76,77] Intuitively, a subsystem M of M contains a subset of states of M, and a transition of M originating in a state of M remains unchanged in M or is redirected to fail (instead of explicitely redirecting to fail, sub-stochastic distributions are used in [76,77] with the same effect). We say that the states S all \S all and the transitions (s, α, t) with P(s, α, t) > 0 and P (s, α, t) = 0 have been deleted in M .…”