@article{CMUC_1968_9_4_a13,
     author = {Frol{\'\i}k, Zden\v{e}k},
     title = {A note on the {Souslin} operations},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {641--650},
     year = {1968},
     volume = {9},
     number = {4},
     mrnumber = {0252230},
     zbl = {0199.30604},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1968_9_4_a13/}
}