@article{10_37236_1270,
     author = {Gilbert Labelle and Pierre Leroux},
     title = {An extension of the exponential formula in enumerative combinatorics},
     journal = {The electronic journal of combinatorics},
     year = {1996},
     volume = {3},
     number = {2},
     doi = {10.37236/1270},
     zbl = {0856.05003},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/1270/}
}