This paper shows how network symmetries (or the graph-theory concept of automorphism) can be used to cluster faults into classes and thus simplify the process of finding a test set: tests for these automorphic classes are found by classical methods and then expanded using automorphisms to produce a test-set. The process does not seem more complex than the classical ones. Furthermore, by using a multilevel description, the process is easily extended to networks of modules.

This correspondence shows how recursion can be used to simplify testing of combinational circuits. Necessary and sufficient conditions for testing simple iterative arrays (one-dimensional) with a fixed number of tests (independent of the number of cells) are given. Multiple faults and diagnosis in such circuits are also studied. The extension of the concept of simple iteration to complex iteration that may realize more complex recursive functions, is defined. Examples of such complex iterative circuits are studied.