@article{MZ_1970__116_171393,
     author = {Michael Barr},
     title = {Coequalizers and {Free} {Triples.}},
     journal = {Mathematische Zeitschrift},
     pages = {307--322},
     publisher = {mathdoc},
     volume = {116},
     year = {1970},
     zbl = {0194.01701},
     url = {http://geodesic.mathdoc.fr/item/MZ_1970__116_171393/}
}