@article{SF_1991__43_3_135117,
     author = {D.A. Jackson},
     title = {On the invariance of small overlap hypotheses.},
     journal = {Semigroup forum},
     pages = {299--304},
     publisher = {mathdoc},
     volume = {43},
     number = {3},
     year = {1991},
     zbl = {0733.20035},
     url = {http://geodesic.mathdoc.fr/item/SF_1991__43_3_135117/}
}