A note on the derivation of maximal common subgraphs of two directed or undirected graphs

In this note the problem is considered of finding maximal common subgraphs of two given graphs. A technique is described by which this problem can be stated as a problem of deriving maximal compatibility classes. A known «maximal compatibility classes» algorithm can then be used to derive maximal common subgraphs.The same technique is shown to apply to the classical subgraph isomorphism problem.