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2. O. Perron, Die Lehre von den Kettenbruchen, Teubner, Stuttgart (1957).
3. P. L. Chebyshev, Collected Works [in Russian], Vol. 3, Izd. Akad. Nauk SSSR, Moscow (1948).
4. A. A. Markov, Selected Papers on Continued Fractions and the Theory of Functions Deviating Least from Zero [in Russian], Gostekhizdat, Moscow (1948).
5. T. Stieltjes, ?Recherches sur les fractions continues,? Ann. Fac. Sci. Univ. Toulouse,8, J1-J122 (1894);9, A1?A47 (1895). [Reprinted in his Oeuvres Completes, Tome 2, Noordhoff (1918), pp. 402?566.]