A Lower Bound for the First Eigenvalue of the Laplacian on a Compact Manifold Ping Li Indiana University Mathematics Journal 1979 text pdf 10.1512/iumj.1979.28.28075 10.1512/iumj.1979.28.28075 en Indiana Univ. Math. J. 28 (1979) 1013 - 1019 state-of-the-art mathematics http://iumj.org/access/