@article{MAN_1978__237_182789,
     author = {Donald J. Collins},
     title = {Presentations of the {Amalgamated} {Free} {Product} of two {Infinite} {Cycles.}},
     journal = {Mathematische Annalen},
     pages = {233--242},
     publisher = {mathdoc},
     volume = {237},
     year = {1978},
     zbl = {0385.20019},
     url = {http://geodesic.mathdoc.fr/item/MAN_1978__237_182789/}
}