sentences:  The degree of a vertex is equal to the number of adjacent vertices.A special case is a loop that connects a vertex to itself; if such an edge exists, the vertex belongs to its own neighbourhood.If all vertices in "G" have neighbourhoods that are isomorphic to the same graph "H", "G" is said to be "locally H", and if all vertices in "G" have neighbourhoods that belong to some graph family "F", "G" is said to be "locally F" (, ).