@article{KYB_1973__9_4_a0,
     author = {Gruska, Jozef},
     title = {On star height hierarchies of context-free languages},
     journal = {Kybernetika},
     pages = {--236},
     publisher = {mathdoc},
     volume = {09},
     number = {4},
     year = {1973},
     mrnumber = {0341941},
     zbl = {0273.68053},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KYB_1973__9_4_a0/}
}