“…First, in PDEs we find various nonlinear differential expressions identified by the theory of compensated compactness, see the seminal work of F. Murat [49] and L. Tartar [59], and the subsequent developments [16,17,25]. New and unexpected phenomena concerning higher integrability of the Jacobian determinants and other null Lagrangians have been discovered [46,29,33,28,21] , and used in the geometric function theory [27,26,1], calculus of variations [58,30], and some areas of applied mathematics, [47,48,62]. Recently a viable theory of existence and improved regularity for solutions of PDEs where the uniform ellipticity is lost, has been built out of the distributional div-curl products and null Lagrangians [25,31] .…”