1. Balbes, R. andDwinger, Ph.,Distributive Lattices, University of Missouri Press, Columbia, 1974.
2. Balbes, R. andHorn, A.,Injective and projective Heyting algebras, Trans. A.M.S.148 (1970), 549?559.
3. Bigard, A., Keimel, K. andWolfenstein, S.,Groupes et anneaux réticulés, LNM 608, Springer-Verlag, Berlin, 1977.
4. Burris, S. andSankappanavar, H. P.,A course in Universal Algebra, Springer Verlag, NYHeidelberg-Berlin, 1981.
5. Cignoli, R.,A Hahn-Banach Theorem for distributive lattices, Revista Unión Matemática Argentina25 (1971), 335?342.