1. C. B. Allendoerfer, Rigidity for spaces of class greater than one, Amer. J. Math. 61 (1939), 633-644.
2. L. Barbosa and M. do Carmo, Stability of Minimal surfaces and eigenvalues of the Laplacian, Math. Z. 173 (1980),13-28.
3. L. Barbosa and M. do Carmo, A necessary condition for a metric in Mft to be minimally immersed in $$ {\mathbb{R}}^{n+1} $$ , An. Acad. Bras. Cienc. 50 (1978), 445-454.
4. E. Calabi, Metric Riemann surfaces, in Contributions to the Theory of Riemann Surfaces, Annals of Math. Studies 30, Princeton University Press 1953, 77-85.
5. E. Calabi, Quelques applications de l’analyse complexe aux surfaces d’aire minima, Topics in Complex Manifolds, Presses de l’Universite de Montreal 1968, 58-81.