@article{CTGDC_1989__30_1_45_0,
     author = {Higgs, Denis},
     title = {Remarks on duality for $\Sigma $-groups. {I.} {Products} and coproducts},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     pages = {45--59},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {30},
     number = {1},
     year = {1989},
     zbl = {0683.20044},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_1989__30_1_45_0/}
}