@article{10_2307_121127,
     author = {Enrique R. Pujals and Mart{\'\i}n Sambarino},
     title = {Homoclinic tangencies and hyperbolicity for surface diffeomorphisms},
     journal = {Annals of mathematics},
     year = {2000},
     volume = {151},
     number = {3},
     doi = {10.2307/121127},
     zbl = {0959.37040},
     url = {http://geodesic.mathdoc.fr/articles/10.2307/121127/}
}