We define a new invariant for shift equivalence of sofic shifts. This invariant, that we call the syntactic graph of a sofic shift, is the directed acyclic graph of characteristic groups of the non null regular D-classes of the syntactic semigroup of the shift.

The Merrifield-Simmons index of a graph is defined as the total number of the independent sets of the graph and the Hosoya index of a graph is defined as the total number of the matchings of the graph. In this paper, we give formula for Merrifield-Simmons and Hosoya indices of some classes of cartesian product of two graphs K{_2}×H, where H is a path graph P{_n}, cyclic graph C{_n}, or star gra...

The independence equivalence class of a graph $G$ is the set graphs that have same polynomial as $G$. A whose contains only itself, up to isomorphism, unique. Beaton, Brown and Cameron (2019) showed paths with an odd number vertices are unique raised problem finding even vertices. completely solved in this paper.