Writing pushdown acceptors

  • Authors:
  • George Mager

  • Affiliations:
  • University of Southern California, Los Angeles, California 90007, USA and System Development Corporation, Santa Monica, California 90406, USA

  • Venue:
  • Journal of Computer and System Sciences
  • Year:
  • 1969

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Abstract

This paper introduces a new automaton, called a writing pushdown acceptor (abbreviated wpda), and investigates some of its properties. A wpda is essentially a two-way pushdown acceptor that can write on its input tape. A number of results about wpda are established. In particular, it is shown thato(1)Each set accepted by a wpda is accepted by some wpda that halts for all inputs. (2)The family of sets accepted by deterministic wpda forms a Boolean algebra of sets, contains the family of context sensitive languages, and properly contains the family of sets accepted by deterministic two-way pushdown acceptors. (3)The family of sets accepted by (deterministic) wpda is contained in the family of sets accepted by (deterministic) stack acceptors. In the deterministic case, the containment is shown to be proper.