@article{MZ_1970__115_171334,
     author = {R. Arthur Knoebel},
     title = {Primal {Extensions} of {Universal} {Algebras.}},
     journal = {Mathematische Zeitschrift},
     pages = {53--57},
     publisher = {mathdoc},
     volume = {115},
     year = {1970},
     zbl = {0182.34302},
     url = {http://geodesic.mathdoc.fr/item/MZ_1970__115_171334/}
}