1. H. AMANN, Periodic solutions of semilinear parabolic problems, Nonlinear Analysis (Cesari-Kannan-Weinberger, eds.), Academic Press, New-York (1978), 1?29
2. H. BREZIS,Opérateurs maximaux monotones et semi-groupes de contractions dans les espaces de Hilbert, North-Holland, Amsterdam/London (1973)
3. H. BREZIS, A. HARAUX. Image d'une somme d'opérateurs monotones et applications, Israel J. Math.23, 2 (1976), 165?186
4. H. BREZIS, L. NIRENBERG. Characterizations of the ranges of some nonlinear operators and applications to boundary value problems, Ann Scuola Norm. Sup. Pisa Série IV, vol. VI (1978), 165?186
5. M. J. ESTEBAN, A remark on the existence of positive periodic solutions of superlinear parabolic problems, Proceedings A.M.S.102, 1 (1988), 131?136