1. [1] Abramowitz, M. and Stegun, I. A., eds., Handbook of mathematical functions with formulas, graphs, and mathematical tables, National Bureau of Standards Applied Mathematics Series, vol. 55, For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 1964.
2. [2] R. A. Adams, Sobolev spaces, Academic Press [A subsidiary of Harcourt Brace Jovanovich, Publishers], New York-London, 1975.
3. [3] M. S. Ashbaugh and R. S. Laugesen, Fundamental tones and buckling loads of clamped plates, preprint, 1994.
4. [4] Gábor Szegő, Collected papers. Vol. 3, Contemporary Mathematicians, Birkhäuser Boston, Mass., 1982.
5. [5] C. Bandle, Isoperimetric inequalities and applications, Monographs and Studies in Mathematics, vol. 7, Pitman (Advanced Publishing Program), Boston, Mass., 1980.