@article{BAG_1987__24_138358,
     author = {Jaak Hion},
     title = {On nets of free polygons over a category and their categories of homomorphisms},
     journal = {Beitr\"age zur Algebra und Geometrie},
     pages = {51--74},
     year = {1987},
     volume = {24},
     zbl = {0612.18003},
     url = {http://geodesic.mathdoc.fr/item/BAG_1987__24_138358/}
}