@article{MM2_1983__43_154951,
     author = {Bernd Herzog},
     title = {A criterion for tangential flatness.},
     journal = {Manuscripta mathematica},
     pages = {219--228},
     publisher = {mathdoc},
     volume = {43},
     year = {1983},
     zbl = {0521.13011},
     url = {http://geodesic.mathdoc.fr/item/MM2_1983__43_154951/}
}