Hoffman, Michael E. Max Planck Institute for Mathematics, Max Planck Society;
http://dx.doi.org/10.1016/j.disc.2015.10.035 (Publisher version)
Hoffman_Updown categories_oa_2016.pdf (Any fulltext), 280KB
Hoffman, M. E. (2016). Updown categories: generating functions and universal covers. Discrete Mathematics, 339(2), 906-922. doi:10.1016/j.disc.2015.10.035.