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2. L. Van Hove in: Preludes in Theoretical Physics, ed. A. De-Shalit, H. Feshbach and L. Van Hove, Amsterdam, 1965.
3. H. P. Dürr, W. Heisenberg, H. Mitter, S. Schlieder andK. Yamazaki, Zeits. f. Naturforsch.,14a, 442, 1959 and subsequent papers.
4. W. Heisenberg: Introduction to the Unified Field Theory of Elementary Particles, to be published.
5. K. Ladányi, Nuovo Cimento,45, 289, 1966.