@article{10_4153_CJM_2005_018_x,
     author = {Wise, Daniel T.},
     title = {Approximating {Flats} by {Periodic} {Flats} in {CAT(0)} {Square} {Complexes}},
     journal = {Canadian journal of mathematics},
     pages = {416--448},
     year = {2005},
     volume = {57},
     number = {2},
     doi = {10.4153/CJM-2005-018-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-2005-018-x/}
}