1. Abramowitz, A., Stegun, I.B.: Handbook of mathematical functions, N.B.S. Applied Math. Series, Vol. 53. Washington, D.C.: 1964
2. Cauer, W.: Bemerkung über eine Extremalaufgabe. Math. Mech.20, 358 (1946)
3. Chiu, Y.H.: An integral equation method of solution of ?u+k 2 u=0 in the exterior of a bounded domain. Ph.D. Thesis, University of Utah, 1976
4. Gon?ar, A.A.: Estimates of the growth of rational functions and some of their applications. Math. U.S.S.R. Sbornik1, 445?456 (1967)
5. Gon?ar, A.A.: On the rapidity of rational approximation of continuous functions with characteristic singularities. Math. U.S.S.R. Sbornik2, 561?568 (1967)