@article{JTNB_2009__21_3_703_0,
     author = {Jouni Parkkonen and Fr\'ed\'eric Paulin},
     title = {On the closedness of approximation spectra},
     journal = {Journal de th\'eorie des nombres de Bordeaux},
     pages = {703--712},
     publisher = {Universit\'e Bordeaux 1},
     volume = {21},
     number = {3},
     year = {2009},
     doi = {10.5802/jtnb.696},
     mrnumber = {2605541},
     zbl = {1205.11083},
     language = {en},
     url = {https://jtnb.centre-mersenne.org/articles/10.5802/jtnb.696/}
}