“…Bénilan, L. Boccardo, T. Gallouet, R. Gariepy, M. Pierre, J.L. Vazquez in [6], this notion was then adapted by many authors to study some nonlinear elliptic and parabolic problems with a constant or variable exponent and Dirichlet or Neumann boundary conditions (see for example [1], [4], [14], [16], [19], and [20]).…”