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2. Pontryagin, L. S., “Topological Groups”, Gordon & Breach, New York, 1966.
3. Robertson, A. P., and W. Robertson, “Topological vector spaces”, Cambridge University Press, 1964.
4. Hofmann, K. H., and P. S. Mostert, “Elements of Compact Semigroups”, Charles E. Merrill, Columbus (Ohio), 1966.