@article{10_4064_fm_134_1_1_14,
     author = {R. Dobre\'nko and Z. Kucharski},
     title = {On the generalization of the {Nielsen} number},
     journal = {Fundamenta Mathematicae},
     pages = {1--14},
     year = {1990},
     volume = {134},
     number = {1},
     doi = {10.4064/fm-134-1-1-14},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-134-1-1-14/}
}