1. Lect. Notes Math.;P. B�rard,1986
2. B�rard, P., Gallot, S.: In�galit�s isop�rimetriques pour l'�quation de la chaleur et applications � l'estimation de quelques invariants g�om�triques. In: S�minaire Goulaouic-Meyer-Schwarz 1983?84. Palaiseau: �cole Polytechnique 1984
3. B�rard Bergery, L., Bourguignon, J.P.: Laplacians and Riemannian submersions with totally geodesic fibers. III. J. Math.26 (n. 2), 181?200 (1982)
4. Lect. Notes Math.;M. Berger,1971
5. Besson, G., Bordoni, M.: On the spectrum of Riemannian submersions with totally geodesic fibers. Rend. Mat. Accad. Naz. Lincei, Ser. IX1, 335?340 (1990)