@article{CMH_1969__44_139408,
     author = {H. Guggenheimer},
     title = {Hill {Equations} with {Coexisting} {Periodic} {Solutions,} {II.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {381--384},
     publisher = {mathdoc},
     volume = {44},
     year = {1969},
     zbl = {0186.41003},
     url = {http://geodesic.mathdoc.fr/item/CMH_1969__44_139408/}
}