@article{10_4007_annals_2015_182_1_2,
     author = {Kyungyong Lee and Ralf Schiffler},
     title = {Positivity for cluster algebras},
     journal = {Annals of mathematics},
     pages = {73--125},
     publisher = {mathdoc},
     volume = {182},
     number = {1},
     year = {2015},
     doi = {10.4007/annals.2015.182.1.2},
     mrnumber = {3374957},
     zbl = {06456006
},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4007/annals.2015.182.1.2/}
}