@article{MM2_1980__31_154711,
     author = {W. Beekmann and Shao-Chien Chang},
     title = {Some {Summability} {Invariants.}},
     journal = {Manuscripta mathematica},
     pages = {363--378},
     publisher = {mathdoc},
     volume = {31},
     year = {1980},
     zbl = {0435.40008},
     url = {http://geodesic.mathdoc.fr/item/MM2_1980__31_154711/}
}