@article{KYB_1975__11_1_a2,
     author = {Gruska, Jozef},
     title = {A note on $\varepsilon$-rules in context-free grammars},
     journal = {Kybernetika},
     pages = {--31},
     publisher = {mathdoc},
     volume = {11},
     number = {1},
     year = {1975},
     mrnumber = {0395317},
     zbl = {0305.68061},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KYB_1975__11_1_a2/}
}