https://katalog.hgb-leipzig.de/Record/0-024351903 Engels, Wolfram:
The optimal monetary unit : Real-asset currency, state monetary sovereignty, and the private issue of bank notes / Wolfram Engels. — Frankfurt [u.a.] : Campus-Verl, 1981. — 134 S; graph. Darst; 8°.
Literaturverz. S. 129 - 134.
ISBN 3593328437, 9783593328430