GIT-A Heuristic Program for Testing Pairs of Directed Line Graphs for Isomorphism* Given a pair of directed line graphs, the problem of ascertaining whether or not they are isomorphic is one for which no efficient algorithmic solution is known. Since a straightforward enumerative algorithm might require 40 years of running time on a very high speed computer in order to compare two 15-node graphs, a more sophisticated approach seems called for. The situation is similar to that prevailing in areas such as game-playing and theorem-proving, where practical algorithms are unknown (for the interesting cases), but where various practical though only partially successful techniques are available. Git-Graph Isomorphism Tester-incorporates a variety of processes that attempt to narrow down the search for an isomorphism, or to demonstrate that none exists. No one scheme is relied upon exclusively for a solution, and the program is designed to avoid excessive computation along fruitless lines. GIT has been written in the COMIT language and successfully tested on the IBM 7090. CACM January, 1964 Unger, S. H. CA640110 JB March 10, 1978 5:24 AM 1145 4 1145 1145 5 1145 1145 5 1145 1145 5 1145 1504 5 1145 3040 5 1145 655 5 1145 1145 6 1145 1145 6 1145