@article{CMUC_1964_5_4_a6,
     author = {Pultr, Ale\v{s}},
     title = {Concerning universal categories},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {227--239},
     year = {1964},
     volume = {5},
     number = {4},
     mrnumber = {0173696},
     zbl = {0135.02101},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1964_5_4_a6/}
}