@article{MM2_1996__89_3_156147,
     author = {Heinrich Steinlein},
     title = {On the {Index} of {Approximating} {Sets} of {Periodic} {Points.}},
     journal = {Manuscripta mathematica},
     pages = {15--34},
     publisher = {mathdoc},
     volume = {89},
     number = {3},
     year = {1996},
     zbl = {0853.54039},
     url = {http://geodesic.mathdoc.fr/item/MM2_1996__89_3_156147/}
}