@article{10_14708_ma_v44i1_829,
     author = {Zdzis{\l}aw Porosi\'nski and Marek Skarupski and Krzysztof Szajowski},
     title = {Duration problem: basic concept and some extensions},
     journal = {Mathematica Applicanda},
     pages = { 87--112},
     publisher = {mathdoc},
     volume = {44},
     number = {1},
     year = {2016},
     doi = {10.14708/ma.v44i1.829},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/articles/10.14708/ma.v44i1.829/}
}