@article{AMLG_1980__20_137968,
     author = {Bernd Koppelberg},
     title = {Ultrapowers and {Boolean} ultrapowers of ... and ...1.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {147--154},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0474.03030},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1980__20_137968/}
}