^Keith Spalding, Gerhard Muller-SchwefeAn Historical Dictionary of German Figurative Usage by Gerhard Muller-Schwefe and Keith Spalding (2000, Paperback, Supplement)ISBN 9780631219118 (revised Sep 2017)
^An Historical Dictionary Of German Figurative Usage, Fascicle 60: SupplementIndigo. ISBN 9780631219118 (revised Jan 2017)