Piecewise testable tree languages

Abstract

This paper presents a decidable characterization of tree languages that can be defined by a boolean combination of Sigma_1 sentences. This is a tree extension of the Simon theorem, which says that a string language can be defined by a boolean combination of Sigma_1 sentences if and only if its syntactic monoid is J-trivial.

Keywords

• computer science - formal languages and automata theory
• f.4.3,f.4.1