If we restrict the transition relation such, that for each pair (q,a) Q there is at most one q' Q as successor state and we set I = 1 then we have a deterministic finite automaton (DFA). Otherwise the automaton is non-deterministic finite automaton (NFA).
THEOREM: For each finite automaton there exists a deterministic and complete one recognizing the same set.
PROOF: Cf. Perrin (1990) [227], P.6.
CORROLARY: The complement of a recognizable set is again a recognizable set.
PROOF: Cf. Perrin (1990) [227], P.6.