  This short note clarifies that the "pinched hysteresis loop" fingerprint of a
memristor, or a memristive device, must hold for all amplitudes, for all
frequencies, and for all initial conditions, of any periodic testing waveform,
such as sinusoidal or triangular signals, which assumes both positive and
negative values over each period of the waveform. We proved that the systems
presented in [1] are not memristive devices because their hysteresis loops are
not pinched at the origin for all amplitudes, and for all initial conditions.
