@article{PORMA_1980__39_1-4_115427,
     author = {Loureiro, Isabel},
     title = {Homomorphism kernels of a tetravalent modal algebra},
     journal = {Portugaliae mathematica},
     pages = {371--379},
     publisher = {mathdoc},
     volume = {39},
     number = {1-4},
     year = {1980},
     mrnumber = {0776249},
     zbl = {0562.03035},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1980__39_1-4_115427/}
}