@article{MZ_1975__143_172213,
     author = {Armin Frei and Peter Hilton and A. Deleanu},
     title = {Idempotent {Triples} and {Completion.}},
     journal = {Mathematische Zeitschrift},
     pages = {91--104},
     year = {1975},
     volume = {143},
     zbl = {0295.18001},
     url = {http://geodesic.mathdoc.fr/item/MZ_1975__143_172213/}
}