摘要
Let M be a complete, simply connected, Riemannian manifold with -k<sub>2</sub><sup>2</sup>≤K<sub>M</sub> ≤k<sub>1</sub><sup>2</sup>,where K<sub>M</sub> is the sectional curvature of M and 0【k<sub>1</sub>【k<sub>2</sub>【+∞. It is known that on such an M the Laplacian may have no L<sup>2</sup>-eigenvalues. Prof Yau conjectured that this should be
