Top panel: observed modes. Middle panel: theoretical modes with ℓ ≤ 2: retrograde (light grey), zonal (dark grey), and prograde (black) modes. Lower panel: stepwise addition of various rotational effects on the mode frequencies in near-degenerate mode perturbation theory (spherical symmetry, linear splitting, non-spherical distortion, and three-mode coupling). Only ℓ = 0,1,2 are shown for clarity as filled circles, squares, and triangles.