@article{10_4153_CMB_1967_039_x,
     author = {Schirmer, Helga},
     title = {Coincidence {Producing} {Maps} {Onto} {Trees}},
     journal = {Canadian mathematical bulletin},
     pages = {417--423},
     year = {1967},
     volume = {10},
     number = {3},
     doi = {10.4153/CMB-1967-039-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1967-039-x/}
}