@article{MAN_1989__285_1_164607,
     author = {Christian C. Fenske},
     title = {An index for periodic orbits of functional differential equations.},
     journal = {Mathematische Annalen},
     pages = {381--392},
     publisher = {mathdoc},
     volume = {285},
     number = {1},
     year = {1989},
     zbl = {0663.34057},
     url = {http://geodesic.mathdoc.fr/item/MAN_1989__285_1_164607/}
}