Some Examples of Semi-rational and Non-semi-rational DAG Languages. Extended Version

Abstract

The class of semi-rational dag (d irected acyclic graph) languages can be equivalently characterized by labeled Petri nets with ε-transitions, by rather simple leave substituting tree grammars with additional non-local merge rules, or as a synchronization closure of Courcelles class of recognizable sets of unranked, unordered trees. However, no direct recognition by some magma is known. For a better understanding, we present here some examples of languages within and without the class of semi-rational dag languages.