Suppose that $M^2$ is a closed Riemannian manifold and that $u$ is a $C^2(M\setminus S),$ where $S$ is a closed measure set consisting possibly on a enumerable amount of points. Can we still conclude that $\int_M\Delta u =0?$
Is $\int_M\Delta u = 0$ if $u$ is not $C^2$ on a set of measure zero?
L.F. Cavenaghi
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