@article{10_1090_S0894_0347_08_00627_9,
     author = {Bjerkl\"ov, Kristian and J\"ager, Tobias},
     title = {Rotation numbers for quasiperiodically forced circle maps-mode-locking vs. strict monotonicity},
     journal = {Journal of the American Mathematical Society},
     pages = {353--362},
     year = {2009},
     volume = {22},
     number = {2},
     doi = {10.1090/S0894-0347-08-00627-9},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-08-00627-9/}
}