The digitization and unrestricted availablity of the backfile of the Bulletin of the American Mathematical Society (1891-1991) is made possible with the generous support of the Gordon and Betty Moore Foundation, the Mathematical Sciences Research Institute, the American Mathematical Society, and Project Euclid.
A proof of the theorem: $\frac{{\partial ^2 u}} {{\partial x\partial y}} = \frac{{\partial ^2 u}} {{\partial y\partial x}}$
J. K. Whittemore. (1900)
Review: Michael Spivak, A comprehensive introduction to differential geometry
Stephanie Alexander. (1978)
