FAN
Beginner
An improved search for test patterns that takes shortcuts where wires split.
Novice
A 1983 refinement of PODEM by Fujiwara and Shimono. It fills in every value that is forced, stops tracing backward at parts of the circuit that can always be satisfied later, and pursues several goals at once.
Expert
Adds immediate implication of uniquely forced values, stops backtrace at headlines (the outputs of fanout-free cones) and propagates through all branches of a fanout, cutting backtracks compared with PODEM.