@article{JEMS_2006_8_2_a15,
     author = {Hiroshi Matano and Paul H. Rabinowitz},
     title = {On the necessity of gaps},
     journal = {Journal of the European Mathematical Society},
     pages = {355--373},
     year = {2006},
     volume = {8},
     number = {2},
     doi = {10.4171/jems/57},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/57/}
}