Cita APA (7a ed.)

Küntzel, G., & Leber, B. (1960). Arthur Schopenhauer. [s.n.].

Cita Chicago Style (17a ed.)

Küntzel, Gerhard, y Beate Leber. Arthur Schopenhauer. [Frankfurt am Main]: [s.n.], 1960.

Cita MLA (9a ed.)

Küntzel, Gerhard, y Beate Leber. Arthur Schopenhauer. [s.n.], 1960.