R. Brooks and ?. , The bottom of the spectrum of a riemannian covering, J. Reine Angew. Math, vol.357, pp.101-114, 1985.

[. Cheng and &. , Isoperimetric inequalities and the gap between the first and second eigenvalues of an Euclidean domain, Journal of Geometric Analysis, vol.8, issue.2, pp.217-239, 1997.
DOI : 10.1007/BF02921721

A. Girouard and &. , Polterovich ? « On the Hersch-Payne-Schiffer inequalities for Steklov eigenvalues, pp.106-117, 2010.

P. Guérini and ?. , Prescription du spectre du laplacien de Hodge-de Rham », Ann. scient. Éc. norm. sup, pp.270-303, 2004.

J. Sylvester and &. , Uhlmann ? « The Dirichlet to Neumann map and applications, Inverse problems in partial differential equations SIAM, pp.101-139, 1989.