“…The Riesz transform ∇∆ −1/2 f , introduced by Strichartz [27] on Euclidean space, has been investigated in many subsequent papers, see e.g., [8,2,3,4] and the references therein, and has been further extended to Riemannian manifolds, e.g. [1,11,12,13,23,29]. Since the Riesz transform is bounded in L 2 (M), by the interpolation theorem, the weak (1, 1) property already implies L p (M)-boundedness for p ∈ (1,2].…”