@article{CMH_1978__53_139742,
     author = {Michael H. Freedman},
     title = {Quadruple points of 3-manifolds in {S4.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {385--394},
     publisher = {mathdoc},
     volume = {53},
     year = {1978},
     zbl = {0404.57011},
     url = {http://geodesic.mathdoc.fr/item/CMH_1978__53_139742/}
}