@article{SLC_2009-2011_61A_a6,
     author = {Gilbert Labelle and C\'edric Lamathe},
     title = {General {Combinatorial} {Differential} {Operators}},
     journal = {S\'eminaire lotharingien de combinatoire},
     year = {2009-2011},
     volume = {61A},
     url = {http://geodesic.mathdoc.fr/item/SLC_2009-2011_61A_a6/}
}