@article{10_1090_S0894_0347_08_00603_6,
     author = {Lusztig, G.},
     title = {Study of a {\ensuremath{\mathbf{Z}}-form} of the coordinate ring of a reductive group},
     journal = {Journal of the American Mathematical Society},
     pages = {739--769},
     year = {2009},
     volume = {22},
     number = {3},
     doi = {10.1090/S0894-0347-08-00603-6},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-08-00603-6/}
}