@article{10_2307_121088,
     author = {Michael Christ and Alexander Nagel and Elias M. Stein and Stephen Wainger},
     title = {Singular and maximal {Radon} transforms: {Analysis} and geometry},
     journal = {Annals of mathematics},
     year = {1999},
     volume = {150},
     number = {2},
     doi = {10.2307/121088},
     zbl = {0960.44001},
     url = {http://geodesic.mathdoc.fr/articles/10.2307/121088/}
}