@article{MM2_1977__21_154455,
     author = {Juhani Nieminen},
     title = {Filters and {Simple} {Graphic} {Algebras.}},
     journal = {Manuscripta mathematica},
     pages = {51--58},
     publisher = {mathdoc},
     volume = {21},
     year = {1977},
     zbl = {0359.06013},
     url = {http://geodesic.mathdoc.fr/item/MM2_1977__21_154455/}
}