E. E. Levi convexity and the Hans Lewy problem. Part I : reduction to vanishing theorems
Ein Existenzsatz über maßtreue Abbildungen.
Entwickelung einiger Eigenschaften der quadratischen Formen von n Differentialen. (Erste Mittheilung).
Entwickelung einiger Eigenschaften der quadratischen Formen von n Differentialen. (Zweite Mittheilung).
Examples from the calculus of variations. III. Legendre and Jacobi conditions
We will deal with a new geometrical interpretation of the classical Legendre and Jacobi conditions: they are represented by the rate and the magnitude of rotation of certain linear subspaces of the tangent space around the tangents to the extremals. (The linear subspaces can be replaced by conical subsets of the tangent space.) This interpretation can be carried over to nondegenerate Lagrange problems but applies also to the degenerate variational integrals mentioned in the preceding Part II.
Existence de l-formes fermées non singulières dans une classe de cohomologie de de Rham