@article{SLC_2009-2011_61A_a11,
     author = {Luca Ferrari and Pierre Leroux},
     title = {ECO {Species}},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {61A},
     year = {2009-2011},
     url = {http://geodesic.mathdoc.fr/item/SLC_2009-2011_61A_a11/}
}