@article{10_37236_187,
     author = {G. Dupont},
     title = {Positivity in coefficient-free rank two cluster algebras.},
     journal = {The electronic journal of combinatorics},
     year = {2009},
     volume = {16},
     number = {1},
     doi = {10.37236/187},
     zbl = {1193.16017},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/187/}
}