@article{MZ_1976__151_172440,
     author = {Ludwig Br\"ocker},
     title = {Characterization of {Fans} and {Hereditarily} {Pythagorean} {Fields.}},
     journal = {Mathematische Zeitschrift},
     pages = {149--164},
     year = {1976},
     volume = {151},
     zbl = {0319.12102},
     url = {http://geodesic.mathdoc.fr/item/MZ_1976__151_172440/}
}