@article{10_1017_S0017089500003530,
     author = {Macdonald, I. D.},
     title = {Groups of breadth four have class five},
     journal = {Glasgow mathematical journal},
     pages = {141--148},
     year = {1978},
     volume = {19},
     number = {2},
     doi = {10.1017/S0017089500003530},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003530/}
}