@article{MZ_1975__145_172290,
     author = {Robert Gulliver},
     title = {Branched {Immersions} of {Surfaces} and {Reduction} of {Topological} {Type,} {I.}},
     journal = {Mathematische Zeitschrift},
     pages = {267--288},
     publisher = {mathdoc},
     volume = {145},
     year = {1975},
     zbl = {0299.57014},
     url = {http://geodesic.mathdoc.fr/item/MZ_1975__145_172290/}
}