@article{10_21136_CMJ_1961_100475,
     author = {Wallace, A. D.},
     title = {Relative invertibility in semigroups},
     journal = {Czechoslovak Mathematical Journal},
     pages = {480--482},
     publisher = {mathdoc},
     volume = {11},
     number = {3},
     year = {1961},
     doi = {10.21136/CMJ.1961.100475},
     mrnumber = {0133810},
     zbl = {0099.25802},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1961.100475/}
}