@article{JGAA_2017_21_2_a2,
     author = {Udo Hoffmann},
     title = {On the {Complexity} of the {Planar} {Slope} {Number} {Problem}},
     journal = {Journal of graph algorithms and applications},
     pages = {183--193},
     year = {2017},
     volume = {21},
     number = {2},
     doi = {10.7155/jgaa.00411},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.7155/jgaa.00411/}
}