@article{MAN_1977__227_162976,
     author = {Heiner Zieschang},
     title = {Generators of {Free} {Product} with {Amalgamation} of two {Infinite} {Cyclic} {Groups.}},
     journal = {Mathematische Annalen},
     pages = {195--222},
     publisher = {mathdoc},
     volume = {227},
     year = {1977},
     zbl = {0333.20024},
     url = {http://geodesic.mathdoc.fr/item/MAN_1977__227_162976/}
}