@article{10_14708_wm_v3i1_2675,
     author = {Z. Opial},
     title = {Elementarny dow\'od pierwszej regu{\l}y {Guldina}},
     journal = {Wiadomo\'sci Matematyczne},
     pages = { 23--28},
     publisher = {mathdoc},
     volume = {3},
     number = {1},
     year = {1959},
     doi = {10.14708/wm.v3i1.2675},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/articles/10.14708/wm.v3i1.2675/}
}