@article{PDM_2009_3_a12,
     author = {O. I. Egorushkin and K. V. Safonov},
     title = {An analitic approach in the theory of context-free languages {Greibach} normal form},
     journal = {Prikladna\^a diskretna\^a matematika},
     pages = {112--116},
     publisher = {mathdoc},
     number = {3},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/PDM_2009_3_a12/}
}