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2. Monografie Matematyczne, Vol. 33;Walfisz, Arnold,1957
3. The lattice-points in a circle;Hua, Loo-keng;Quart. J. Math. Oxford Ser.,1942
4. E. Landau, Vorlesungen üeber Zahlentheorie, Von S. Hirzel, Leipzig, 1927, p. 264.
5. Hilbert & Cohn-Vossen, Anschauliche Geometrie, Dover, New York, 1944. p. 29.