@article{JRAM_1990__410_153263,
     author = {Ian F. Putnam},
     title = {The invertible elements are dense in the irrational rotation {C*-algebras.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {160--166},
     publisher = {mathdoc},
     volume = {410},
     year = {1990},
     zbl = {0697.46027},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1990__410_153263/}
}