@article{SF_1980__20_134422,
     author = {F.P. Pedersen and W.S. Sizer},
     title = {Subsemigroups of the finite complexes of a group.},
     journal = {Semigroup forum},
     pages = {285--292},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0456.20035},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__20_134422/}
}