@article{SF_1986__33_134815,
     author = {D. Blagojevic},
     title = {Unions of dihedral groups.},
     journal = {Semigroup forum},
     pages = {293--298},
     publisher = {mathdoc},
     volume = {33},
     year = {1986},
     zbl = {0584.20054},
     url = {http://geodesic.mathdoc.fr/item/SF_1986__33_134815/}
}