@article{10_4064_cm_9_2_171_182,
     author = {Roman Sikorski},
     title = {On open theories},
     journal = {Colloquium Mathematicum},
     pages = {171--182},
     publisher = {mathdoc},
     volume = {9},
     number = {2},
     year = {1962},
     doi = {10.4064/cm-9-2-171-182},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-9-2-171-182/}
}