@article{AULFM_1989_03_a5,
     author = {Libicka, Inga and {\L}azarow, Ewa},
     title = {The {Symetrie} {I-Approximate} {Derivatives}},
     journal = {Acta Universitatis Lodziensis. Folia Mathematica},
     publisher = {mathdoc},
     volume = {03},
     year = {1989},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/item/AULFM_1989_03_a5/}
}