[1] Barthel D., Kümritz R.: Laplacian with a potential. Preprint TU Berlin. MR 0636262

[2] Gallot S., Meyer D.: Opérateur de courbure et laplacien. J. Math. Pures Appl., 54, 259-284 (1975). MR 0454884 | Zbl 0316.53036

[3] Iwasaki I., Katase K.: On the Spectra of Laplace Operator on $\Lambda \sp{*} (S\sp{n})$. Proc. Japan Acad., 55, Sér. A, 141-145 (1979). MR 0533709