@article{10_4064_am_3_3_4_258_284,
     author = {J. Perkal},
     title = {O d{\l}ugo\'sci krzywych empirycznych},
     journal = {Applicationes Mathematicae},
     pages = {258--284},
     publisher = {mathdoc},
     volume = {3},
     number = {3},
     year = {1958},
     doi = {10.4064/am-3-3-4-258-284},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/am-3-3-4-258-284/}
}