@article{701667,
     title = {Coherence constraints for operads, categories and algebras},
     booktitle = {Proceedings of the 20th Winter School "Geometry and Physics"},
     series = {GDML\_Books},
     publisher = {Circolo Matematico di Palermo},
     address = {Palermo},
     year = {2001},
     pages = {29-57},
     mrnumber = {MR1826679},
     zbl = {0984.18007},
     url = {http://dml.mathdoc.fr/item/701667}
}

Markl, Martin; Shnider, Steve. Coherence constraints for operads, categories and algebras, dans Proceedings of the 20th Winter School "Geometry and Physics", GDML_Books,  (2001), pp. 29-57. http://gdmltest.u-ga.fr/item/701667/