The Hilbert Transform on the Two-Sphere: A Spectral Characterization
@techreport{fleischman2010sphere,
  author = 		 {O.Fleischmann and G. Sommer},
  title = 		 {{T}he {H}ilbert {T}ransform on the
{T}wo-{S}phere: {A} {S}pectral {C}haracterization},
  year = {2009},
}