@article{PORMA_1983__42_4_115556,
     author = {Artikis, Theodore},
     title = {An operator for characteristic functions},
     journal = {Portugaliae mathematica},
     pages = {409--416},
     publisher = {mathdoc},
     volume = {42},
     number = {4},
     year = {1983},
     mrnumber = {0836119},
     zbl = {0583.60018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1983__42_4_115556/}
}