@article{SLC_1981_05_a4,
     author = {Joe Gillis and Bruce Reznick and Doron Zeilberger},
     title = {On {Elementary} {Methods} in {Positivity} {Theory}},
     journal = {S\'eminaire lotharingien de combinatoire},
     year = {1981},
     volume = {05},
     url = {http://geodesic.mathdoc.fr/item/SLC_1981_05_a4/}
}