1. P. A. M. Dirac:Proc. Roy. Soc., A268, 57 (1962).
2. A. O. Barut:Relativistic composite systems and extensible models of fields and particles, inProceedings of International Symposium on Mathematical Physics, edited byK. Maurin andR. R≸czka (Holland, 1975).
3. A. O. Barut andG. Bornzin:Nucl. Phys.,81 B, 477 (1974).
4. Cf. the so-called «dual string model of hadrons», reviewed byC. Rebbi:Phys. Rep.,12 C, 1 (1974).
5. R. R≸czka:Global solutions of nonlinear equations for the scalar quantum field for polynomial and nonpolynomial interactions, preprint I.C./72/106, Sect. III. D.