@article{GT_2008_12_4_a2,
     author = {Calegari, Danny},
     title = {Surface subgroups from homology},
     journal = {Geometry & topology},
     pages = {1995--2007},
     publisher = {mathdoc},
     volume = {12},
     number = {4},
     year = {2008},
     doi = {10.2140/gt.2008.12.1995},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/gt.2008.12.1995/}
}