@article{AFST_2012_6_21_2_259_0,
     author = {Lucas, F. and Madden, J. and Schaub, D. and Spivakovsky, M.},
     title = {Approximate roots of a valuation and the {Pierce-Birkhoff} conjecture},
     journal = {Annales de la Facult\'e des sciences de Toulouse : Math\'ematiques},
     pages = {259--342},
     publisher = {Universit\'e Paul Sabatier, Institut de math\'ematiques},
     address = {Toulouse},
     volume = {Ser. 6, 21},
     number = {2},
     year = {2012},
     doi = {10.5802/afst.1336},
     zbl = {1271.13051},
     mrnumber = {2978097},
     language = {en},
     url = {http://archive.numdam.org/articles/10.5802/afst.1336/}
}