@article{JCA_1998_5_1_a7,
     author = {P. Pedregal and V. Sverak},
     title = {A {Note} on {Quasiconvexity} and {Rank-One} {Convexity} for 2x2 {Matrices}},
     journal = {Journal of convex analysis},
     pages = {107--118},
     publisher = {mathdoc},
     volume = {5},
     number = {1},
     year = {1998},
     url = {http://geodesic.mathdoc.fr/item/JCA_1998_5_1_a7/}
}