Claudio Citrini

Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass compilers. We focus on deterministic chains, since nondeterministic transducer chains of length two define the recursively enumerable sets. Deterministic chains recognize in linear time a superset of context-free deterministic languages. This family is $\mathcal{CH}$ closed under Boolean operations, disjoint shuffle,and reverse deterministic pushdown translation, but not under homomorphism. Equivalent definitions of the family in terms of composition of syntax-directed translation schemes and control languages are considered. The family is a strict hierarchy ordered by the length of the chain. The complexity of $\mathcal{CH}$ is obviously linear, but not all linear-time parsable languages are in $\mathcal{CH}$. On the other hand it strictly includes the Boolean closure of deterministic languages. Finally $\mathcal{CH}$ is not comparable with another classical Boolean algebra of formal languages, namely real-ti...

Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass compilers. We focus on deterministic chains, since nondeterministic transducer chains of length two define the recursively enumerable sets. Deterministic chains recognize in linear time a superset of context-free deterministic languages. This family is $\mathcal{CH}$ closed under Boolean operations, disjoint shuffle,and reverse deterministic pushdown translation, but not under homomorphism. Equivalent definitions of the family in terms of composition of syntax-directed translation schemes and control languages are considered. The family is a strict hierarchy ordered by the length of the chain. The complexity of $\mathcal{CH}$ is obviously linear, but not all linear-time parsable languages are in $\mathcal{CH}$. On the other hand it strictly includes the Boolean closure of deterministic languages. Finally $\mathcal{CH}$ is not comparable with another classical Boolean algebra of formal languages, namely real-ti...

Several examples of Saint Augustin’s learning in sciences are reported. They show his constant research of the truth both in human rational knowledge and in faith, which must never be in disagreement. He always tries to overcome, with sometimes straightforward and sometimes sophistic arguments, any inconsistency of the scientific knowledge with the literal or allegoric interpretation of the Holy Scriptures.

ABSTRACT . A new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones is introduced. These languages preserve some important properties of cf languages: a generalization of the Chomsky-Schutzenberger homomorphic characterization theorem, the Parikh theorem and a "pumping lemma" are proved. Multi-push-down languages are an AFL. Their recognizers are automata equipped with a multi-push-down tape. Multi-push-down languages form a hierarchy based on the number of push-down tapes. 1 Introduction This research studies a new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones [14], taking a new direction. We hasten to say that this generalization has nothing to do with past proposals to increase the generative capacity of type 2 grammars by introducing some sort of context-dependency, as for instance in matrix grammars [12, 20] or in other regulated rewriting syst...