On the Differentiability of Functions of Several Variables

The identity of weak and strong extensions of differential operators

Kurt Friedrichs · Transactions of the American Mathematical Society · 1944 · 331 citations

Natural Sciences, Mathematics, Differential Equations +11

Estimates and existence of solutions of elliptic equations

Louis Nirenberg · Communications on Pure and Applied Mathematics · 1956 · 63 citations

Natural Sciences, Mathematics, Differential Equations +9

Non-parametric surfaces given by linearly continuous functions

Casper Goffman · Acta Mathematica · 1960 · 14 citations · Full text

Natural Sciences, Mathematics, Geometry +7