@article{JGG_2011_15_2_JGG_2011_15_2_a1,
     author = {P. Haukkanen and J. K. Merikoski and T. Tossavainen },
     title = {Axiomatizing {Perpendicularity} and {Parallelism}},
     journal = {Journal for geometry and graphics},
     pages = {129--139},
     publisher = {mathdoc},
     volume = {15},
     number = {2},
     year = {2011},
     url = {http://geodesic.mathdoc.fr/item/JGG_2011_15_2_JGG_2011_15_2_a1/}
}