@article{DMTCS_2015_special_285_a36,
     author = {Zhang, Yan X},
     title = {Four {Variations} on {Graded} {Posets}},
     journal = {Discrete mathematics & theoretical computer science},
     publisher = {mathdoc},
     volume = {DMTCS Proceedings, 27th International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2015)},
     year = {2015},
     doi = {10.46298/dmtcs.2492},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.46298/dmtcs.2492/}
}