Blackhole State-Controlled Regulated Pushdown Automata

In this paper, we introduce and study a variant of regulated pushdown automata, called blackhole state-controlled R-PDA where a symbol can always be pushed to the pushdown, but only a given depth of the pushdown contents is remembered; the rest of the pushdown contents is lost. In addition, the automaton can check the form of its pushdown contents according to a given control language. We present characterizations of several language families in terms of these constructs.