@article{SF_1993__47_2_135266,
     author = {M.V. Lawson},
     title = {Congruences on ordered groupoids.},
     journal = {Semigroup forum},
     pages = {150--167},
     publisher = {mathdoc},
     volume = {47},
     number = {2},
     year = {1993},
     zbl = {0790.06015},
     url = {http://geodesic.mathdoc.fr/item/SF_1993__47_2_135266/}
}