References
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- Hile , G.N. and Protter , M.H. 1980 . Inequalities for eigenvalues of the Laplacian . Indiana Univ. Math. J , 29 : 523 – 538 .
- Hile , G.N. and Yeh , R.Z. 1984 . Inequalities for eigenvalues of biharmonic operator . Pacific J. Math , 112 : 115 – 133 .