@article{TAC_2017_32_a22,
     author = {Mark V. Lawson and Alistair R. Wallis},
     title = {Levi categories and graphs of groups},
     journal = {Theory and applications of categories},
     pages = {780--802},
     publisher = {mathdoc},
     volume = {32},
     year = {2017},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2017_32_a22/}
}