 They are neither current nor voltage sources, yet both at the same time.Inserting a nullator in a circuit schematic imposes a "mathematical constraint" on how that circuit must behave, forcing the circuit itself to adopt whatever arrangements needed to meet the condition.For example, the inputs of an ideal operational amplifier (with negative feedback) behave like a nullator, as they draw no current and have no voltage across them, and these conditions are used to analyze the circuitry surrounding the operational amplifier.