@article{SF_1975__10_134099,
     author = {H. Hamilton},
     title = {Permutability of congruences on commutative semigroups.},
     journal = {Semigroup forum},
     pages = {55--66},
     publisher = {mathdoc},
     volume = {10},
     year = {1975},
     zbl = {0298.20061},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__10_134099/}
}