Original sentence: ...how many equivalent transforms of a useful circuit were found by mathematician Ronald Foster when told by AT&T to find all the equivalents before patenting any of them.Articles to link.Composite image filter (Bode circuit).DYK hook.Electrical impedance (from combinations section).Equivalent circuit.It was an enormous 83,539.Network analysis (electrical circuits).Series and parallel circuits.[[Category:Analog circuits]].[[Category:Circuit theorems]].[[Category:Electronic design]].[[Category:Filter theory]]