Let (M,g) be a riemannian manifold with boundary ∂M, the Green operator is the inverse of the Laplacian operator Δϕ=f on M and ϕ=0 on ∂M. Then have we the decomposition:
G(ϕ)(x)=∫Mg(x,y)ϕ(y)dy+∫∂M<ˆg(x,y),dϕ(y)>dy
g is the Green function, and ˆg is the boundary part.