@article{DMTCS_2005_special_251_a3,
     author = {Kozik, Jakub},
     title = {Undecidable problems concerning densities of languages},
     journal = {Discrete mathematics & theoretical computer science},
     publisher = {mathdoc},
     volume = {DMTCS Proceedings vol. AF, Computational Logic and Applications (CLA '05)},
     year = {2005},
     doi = {10.46298/dmtcs.3471},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.46298/dmtcs.3471/}
}