Predavatelj: Ivan Gutman – Kragujevac, Yugoslavia

If G is a graph with vertex set V and edge set E, then the LINE GRAPH of G, denoted by L(G), is the graph whose vertex set is E and in which two vertices are adjacent if the corresponding edges in G touch each other. The ITERATED LINE GRAPH SEQUENCE (ILGS) of the graph G is the sequence G, L(G), L(L(G)), L(L(L(G))), … .
We establish the basic properties of ILGS, especially those related to the number of vertices of the members of the ILGS. Some unsolved problems are pointed out.