@article{SF_1980__19_134387,
     author = {J. Yuan},
     title = {A note on angular semigroups.},
     journal = {Semigroup forum},
     pages = {261--266},
     publisher = {mathdoc},
     volume = {19},
     year = {1980},
     zbl = {0428.43002},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__19_134387/}
}