1. The differentiability of solutions of certain variational problems for multiple integrals, unpublished paper; see C. B. Morrey [15].
2. and , Methods of Mathematical Physics, Vol. 2, Wiley-Interscience, New York, 1962, pp. 320–322 and 326–331.
3. Sulla differentiabilità e l'analiticità delle estremali degli integrali multipli regolari, Mem. Accad. Sci. Torino, s. III, parte I, 1957, pp. 25–43.
4. Normal and Integral Currents
5. A theorem of Lichtenstein