Equational and recognizable sets of graphs
The general algebraic notions of both equational and recognizable sets have been defined in Chapter 3. In this chapter, we apply them to the graph algebras of Chapter 2 and give examples that are interesting from the graph theoretic point of view. We also review the consequences of the results of Chapter 3 and establish some properties that are particular to graph algebras.
In Section 4.1, we study the equational sets of the algebra ; these are called the HR-equational sets. We establish decidability results for membership, emptiness and finiteness, and show some relationships between tree-width and ...