@article{AL_1973_12_6_a6,
     author = {L. Hay},
     title = {Index sets in $O\,'$},
     journal = {Algebra i logika},
     pages = {713--729},
     year = {1973},
     volume = {12},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AL_1973_12_6_a6/}
}