Harmonic Function: A function which is twice continuously differentiable and satisfies Laplace’s equation. Partial Differential Equation (PDE): An equation involving partial derivatives of an ...

Viet Ngo, A Structure Theorem for Discontinuous Derivations of Banach Algebras of Differential Functions, Proceedings of the American Mathematical Society, Vol. 102, No. 3 (Mar., 1988), pp. 507-513 ...