@article{ Solr-acta15878, title = {Congruences on free commutative semigroups}, series = {Acta scientiarum mathematicarum}, author = {Grillet Pierre Antoine}, year = {2001}, url = {http://acta.bibl.u-szeged.hu/15878/1/math_067_numb_003_004_629-672.pdf} }