@article{10_4064_fm189_3_2,
     author = {Patrice Le Calvez},
     title = {Multivalued {Lyapunov} functions for homeomorphisms of the 
2-torus},
     journal = {Fundamenta Mathematicae},
     pages = {227--253},
     publisher = {mathdoc},
     volume = {189},
     number = {3},
     year = {2006},
     doi = {10.4064/fm189-3-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm189-3-2/}
}