  We present an algorithm which modifies a deterministic pushdown automaton
(DPDA) such that (i) the marked language is preserved, (ii) lifelocks are
removed, (iii) deadlocks are removed, (iv) all states and edges are accessible,
and (v) operational blockfreeness is established (i.e., coaccessibility in the
sense that every initial derivation can be continued to a marking
configuration). This problem can be trivially solved for deterministic finite
automata (DFA) but is not solvable for standard petri net classes. The
algorithm is required for an operational extension of the supervisory control
problem (SCP) to the situation where the specification in modeled by a DPDA.
