Heckmanns, F. W., & Schumacher, U. Günther Uecker.
Cita Chicago (17th ed.)Heckmanns, Friedrich W., i Ulrich Schumacher. Günther Uecker.
Cita MLA (8th ed.)Heckmanns, Friedrich W., i Ulrich Schumacher. Günther Uecker.
Atenció: Aquestes cites poden no estar 100% correctes.