@article{ZNSL_2003_302_a12,
     author = {A. V. Shutov},
     title = {The number of words of a~given length in the planar crystallographic groups},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {188--197},
     publisher = {mathdoc},
     volume = {302},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2003_302_a12/}
}