@article{10_4064_cm_7_2_155_160,
     author = {Vera S\'os},
     title = {On a problem of {S.} {Hartman} about normal forms},
     journal = {Colloquium Mathematicum},
     pages = {155--160},
     publisher = {mathdoc},
     volume = {7},
     number = {2},
     year = {1959},
     doi = {10.4064/cm-7-2-155-160},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-7-2-155-160/}
}