@article{PORMA_1988__45_4_115639,
     author = {Sequeira, Margarida},
     title = {Varieties of {Ockham} algebras satisfying $x\le f^4(x)$},
     journal = {Portugaliae mathematica},
     pages = {369--391},
     publisher = {mathdoc},
     volume = {45},
     number = {4},
     year = {1988},
     mrnumber = {0982906},
     zbl = {0678.06006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1988__45_4_115639/}
}