@article{10_4064_cm_43_2_373_381,
     author = {J. P{\l}onka},
     title = {On k-closure operators in graphs},
     journal = {Colloquium Mathematicum},
     pages = {373--381},
     publisher = {mathdoc},
     volume = {43},
     number = {2},
     year = {1980},
     doi = {10.4064/cm-43-2-373-381},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-43-2-373-381/}
}