@article{SLC_2005-2007_54A_a4,
     author = {Fred Butler},
     title = {Symmetry and {Unimodality} in the {q,x,y-Hit} {Numbers}},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {54A},
     year = {2005-2007},
     url = {http://geodesic.mathdoc.fr/item/SLC_2005-2007_54A_a4/}
}