We will use Krasner's notion of a graduation introduced 1940’s in his paper:
[1] Krasner, M.: Une généralisation de la notion de corps-corpoide. Un corpoide remarquable de la théorie des corps valués, C.R. Acad. Sci., Paris 219 (1944), 345-347.
but can be found also in his paper:
[2] Krasner, M.; Anneaux gradués généraux, Colloque d'algèbre, Renns (1980), p. 209-308,
and for paragraded structures introduced first by M. Krasner and M. Vuković
[3] Krasner, M.; Vuković, M.: Structures paragraduées (groupes, anneaux, modules), Queen's Papers in Pure and Applied Mathematics, Queen's University Kingston, ONT, CanCanada, (1987), pp. 163.
[4] Vuković, M.: Structures graduées et paragraduées, Prepublication de l’Institut Fourier, Université de Grenoble I, No. 536 (2001), pp. 1-40