“…Using viscosity solutions (for the general theory of viscosity solution we suggest the references [3,7,15]), one can prove that a weak form of integrability still holds, see, for instance, [2,6,[8][9][10][11][12][13]19], or [20]. As demonstrated in context of homogenization of Hamilton-Jacobi equations, in the classic but unpublished paper by Lions et al [27], equation (1.2) admits viscosity solutions.…”