@article{RCM_2019_53_2_a6,
     author = {Arnold Oostra},
     title = {Existential {Graphs} on nonplanar surfaces},
     journal = {Revista colombiana de matematicas},
     pages = {205--219},
     year = {2019},
     volume = {53},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/RCM_2019_53_2_a6/}
}