@article{10_4064_ba54_3_7,
     author = {Mati Abel and Wies{\l}aw \.Zelazko},
     title = {Topologically {Invertible} {Elements} and {Topological} {Spectrum}},
     journal = {Bulletin of the Polish Academy of Sciences. Mathematics},
     pages = {257--271},
     publisher = {mathdoc},
     volume = {54},
     number = {3},
     year = {2006},
     doi = {10.4064/ba54-3-7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ba54-3-7/}
}