Characterizations of second-order differential operators

Włodzimierz Fechner, Eszter Gselmann, Aleksandra Świątczak

{Let $N,k$ be positive integers with $k\ge 2$, and $\Omega \subset {\mathbb{R}}^N$ be a domain.} By the well-known properties of the Laplacian and the gradient, we have \[ Δ(f\cdot g)(…