@article{MAN_1979__246_163339,
     author = {Fumio Kubo and Tsuyoshi Ando},
     title = {Means of {Positive} {Linear} {Operators.}},
     journal = {Mathematische Annalen},
     pages = {205--224},
     publisher = {mathdoc},
     volume = {246},
     year = {1979},
     zbl = {0412.47013},
     url = {http://geodesic.mathdoc.fr/item/MAN_1979__246_163339/}
}