@article{SF_1977__15_134252,
     author = {B. Madison and J. Stepp},
     title = {Inversion and joint continuity in semigroups on   kw-spaces.},
     journal = {Semigroup forum},
     pages = {195--198},
     year = {1977},
     volume = {15},
     zbl = {0378.22001},
     url = {http://geodesic.mathdoc.fr/item/SF_1977__15_134252/}
}