Have you got any ideas or can you help me in proving this theorem please ?


Let 1\leq p\leq \propto , if u \in C^{2}(R^{n}), \Delta u=0 in {R^{n}} and u \in L^{p}(R^{n}).


So \int_{R^{n}} \left | u(x) \right |^{p}\leq \propto


Prove that: u \equiv 0 in R^{n}