@article{MAN_1983__264_163774,
     author = {Frank Hansen},
     title = {Means and {Concave} {Products} of {Positive} {Semi-Definite} {Matrices.}},
     journal = {Mathematische Annalen},
     pages = {119--128},
     publisher = {mathdoc},
     volume = {264},
     year = {1983},
     zbl = {0495.47021},
     url = {http://geodesic.mathdoc.fr/item/MAN_1983__264_163774/}
}