Revisiting the Rellich inequality

We revisit the Rellich inequality from viewpoint of isolating contributions radial and spherical derivatives. This naturally leads to a comparison norms Laplacian Laplace–Beltrami operators with standard Laplacian. In case operator, three-dimensional is most subtle here we improve result Evans Lewis by identifying best constant. Our arguments build on certain identities recently established Wadade second third authors, along use harmonics.