“…For the sake of clarity, note that by a [classical] solution we hereafter mean a pair (u, P) with u of class C 2 (U, R n ) ∩ C (U, R n ) and P of class C 1 (U) ∩ C (U) such that (1.2) holds in a pointwise sense in U. a Now, proceeding forward and arguing either formally and in a distributional sense, or classically, upon assuming further differentiability on L F , it is seen from (1.2)- Note, however, that this condition alone, unless U has a particular homology, does not imply that L F [u] is a gradient field in U, here, ∇P. For more on the background formulation and applications of system (1.2)-(1.3), in particular to function theory, mechanics, and nonlinear elasticity, see [2,3,5,10,14,19] and [1,4,7,11,12,[15][16][17][18] as well as [20][21][22][23][24][25][26][27]30] and [9,13,29,31,32] for related results and further applications.…”