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@article{PORMA_1992__49_2_115790, author = {Figallo, Aldo V.}, title = {On the congruences in four-valued modal algebras}, journal = {Portugaliae mathematica}, pages = {249--261}, publisher = {mathdoc}, volume = {49}, number = {2}, year = {1992}, mrnumber = {1201977}, zbl = {0787.03060}, language = {en}, url = {http://geodesic.mathdoc.fr/item/PORMA_1992__49_2_115790/} }
Figallo, Aldo V. On the congruences in four-valued modal algebras. Portugaliae mathematica, Tome 49 (1992) no. 2, pp. 249-261. http://geodesic.mathdoc.fr/item/PORMA_1992__49_2_115790/