@article{10_1017_S0017089500007515,
     author = {Gilbert, N. D. and Higgins, P. J.},
     title = {The non-abelian tensor product of groups and related constructions},
     journal = {Glasgow mathematical journal},
     pages = {17--29},
     year = {1989},
     volume = {31},
     number = {1},
     doi = {10.1017/S0017089500007515},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500007515/}
}