1. P. B. Burt:Acta Physiol. Pol. B,7, 617 (1976); inNonlinear Equations in Physics and Mathematics, edited byA. O. Barut (Dordrecht, 1978).
2. P. B. Burt:Quantum Mechanics and Nonlinear Waves (New York, N. Y., 1981).
3. P. B. Burt:Lett. Nuovo Cimento,28, 5 (1980).