@article{MS2_1971__28_166169,
     author = {Jens Peter Reus Christensen},
     title = {Borel {Structures} in {Groups} and {Semigroups.}},
     journal = {Mathematica Scandinavica},
     pages = {124--128},
     publisher = {mathdoc},
     volume = {28},
     year = {1971},
     zbl = {0217.08502},
     url = {http://geodesic.mathdoc.fr/item/MS2_1971__28_166169/}
}