@article{BMMS_2010_33_2_a4,
     author = {Aidan Sims and Samuel B. G. Webster},
     title = {A {Direct} {Approach} to {Co-Universal} {Algebras} {Associated} to {Directed} {Graphs}},
     journal = {Bulletin of the Malaysian Mathematical Society},
     year = {2010},
     volume = {33},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/BMMS_2010_33_2_a4/}
}