Certain 'inconsistencies' in the derivation of the Zitterbewegung solution for Heisenberg equations for the Dirac electron, reported by Sherry (see ibid., vol.9, p.301-2 (1988)) are shown to be incorrect.
Progress of Theoretical Physics Vol. 34 No. 3 (1965) pp. 462–472 Explicit Representation of the Transformation Property of Physical Quantity of Dirac Electron with the Hyperbolic Metric of Velocity Hisaiti Yamasaki Progress of Theoretical Physics Vol. 36 No. 1 (1966) pp. 72–85 A New Derivation of Classical Models of the Spinning Electron from the WKB Solutions to the Pauli and Dirac Equations Hisaiti Yamasaki Progress of Theoretical Physics Vol. 39 No. 2 (1968) pp. 372–393 The Frenkel-Kramers Model and the Zitterbewegung in the Extended Heisenberg Picture of the Dirac Electron Hisaiti Yamasaki