Distribution in the ⟨μ⟩_e, R_e, M_g tridimensional space of E (dark red), cD (purple), dE (green), cE (black) galaxies using their single-Sérsic fits, and of the bulges of all lenticular and spiral types from bulge and disk decompositions color-coded by B/T_g, the bulge-to-total luminosity ratio in the g band. Two different views are shown on the left and right, in order to highlight the fact that galaxies are distributed along a plane, as predicted from Eq. (12), with a small dispersion around it due to redshift: the gray plane is drawn for z = 0 and is best seen in the left panel. The Kormendy and size–luminosity relations are projections against the corresponding faces of the cube.