“…However, for n 3, these three notions of convexity are generally not equivalent [20,42]. For n = 2, on the other hand, it is still an open question whether rank-one convexity implies quasiconvexity [6,8,13,18,21,31,[33][34][35]39]. In fact, many classes of functions on R 2×2 have been identified for which rank-one convexity even implies polyconvexity [7,19,25,26,32] and thus quasiconvexity.…”