@article{10_4171_dm_183,
     author = {Digen Zhang and Manfred Knebusch},
     title = {Convexity, valuations and {Pr\"ufer} extensions in real algebra},
     journal = {Documenta mathematica},
     pages = {1--109},
     year = {2005},
     volume = {10},
     doi = {10.4171/dm/183},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/183/}
}