@article{JGG_2018_22_1_JGG_2018_22_1_a3,
     author = {P. Daugulis },
     title = {Classification and {Normal} {Forms} of {Planar} {4-Multisets} and {Quadrangles}},
     journal = {Journal for geometry and graphics},
     pages = {31--39},
     publisher = {mathdoc},
     volume = {22},
     number = {1},
     year = {2018},
     url = {http://geodesic.mathdoc.fr/item/JGG_2018_22_1_JGG_2018_22_1_a3/}
}