@article{CMUC_1988_29_1_a3,
     author = {Tzouvaras, Athanossios},
     title = {Definability degrees for classes in the alternative set theory},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {41--48},
     year = {1988},
     volume = {29},
     number = {1},
     mrnumber = {937547},
     zbl = {0646.03049},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1988_29_1_a3/}
}