@article{00918293,
title = {A forbidden-suborder characterization of binarily-composable diagrams in double categories.},
journal = {Theory and Applications of Categories [electronic only]},
volume = {1},
year = {1995},
pages = {146-155},
zbl = {0857.18008},
language = {en},
url = {http://dml.mathdoc.fr/item/00918293}
}
Dawson, Robert. A forbidden-suborder characterization of binarily-composable diagrams in double categories.. Theory and Applications of Categories [electronic only], Tome 1 (1995) pp. 146-155. http://gdmltest.u-ga.fr/item/00918293/