Pinched Hysteresis Loops is the Fingerprint of Memristive Devices
  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. 
Hyongsuk Kim, Maheshwar Pd. Sah, and Shyam Prasad Adhikari
cond-mat.mes-hall