@article{AFM_1964_336-344_a5,
     author = {Arto Salomaa},
     title = {On essential variables of functions, especially in the algebra of logic},
     journal = {Annales Fennici Mathematici},
     publisher = {mathdoc},
     volume = {336-344},
     year = {1964},
     doi = {10.5186/aasfm.1964.339},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1964.339/}
}