@article{PORMA_1966__25_2_114976,
     author = {Olson, F.R.},
     title = {An extension of a theorem of {Nielsen}},
     journal = {Portugaliae mathematica},
     pages = {63--66},
     publisher = {mathdoc},
     volume = {25},
     number = {2},
     year = {1966},
     mrnumber = {0210655},
     zbl = {0149.28401},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1966__25_2_114976/}
}