Identifying Unrecognizable Regular Languages by Queries

We describe a new technique useful in identifying a subclass of regular trace languages (defined on a free partially commutative monoid). We extend an algorithm defined by Dana Angluin in 1987 for DFA's and using equivalence and membership queries. In trace languages the words are equivalence classes of strings, and we show how to extract, from a given class, a string that can drive the original learning algorithm. In this way we can identify a class of regular trace languages which includes languages which are not recognizable by any automaton.

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