SPECIAL TYPES OF ACCEPTORS

This chapter discusses three specialized acceptor models: (1) pebble acceptors, which cannot rewrite their input but can make marks on it, with the restriction that only a bounded number of these marks can exist at any given time, (2) pushdown acceptors, which cannot rewrite their input but can store a string of symbols in such a way that only the last symbol in the string can be read, and (3) parallel/sequential acceptors, which are one-dimensional cellular acceptors that read one row of a rectangular input array at a time and move up and down to scan the array. A class of acceptors, called pebble acceptors or marking acceptors, have limited writing ability. Such an acceptor can make marks on its input, but only a bounded number of these marks can exist at any given time.