The Decidability of Equivalence for Determistic Stateless Pushdown Automata Michio Oyamaguchi Namio Honda 367-376 Information and Control September 1978 38 3 db/journals/iandc/iandc38.html#OyamaguchiH78 http://dx.doi.org/10.1016/S0019-9958(78)90139-0