@article{DMGAA_2018_38_1_a9,
     author = {Gr\"atzer, G.},
     title = {Congruences and {Trajectories} in {Planar} {Semimodular} {Lattices}},
     journal = {Discussiones Mathematicae. General Algebra and Applications},
     pages = {131--142},
     publisher = {mathdoc},
     volume = {38},
     number = {1},
     year = {2018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DMGAA_2018_38_1_a9/}
}