Cita APA (7th ed.)

Klaus, G. (1968). Was ist - was soll. Urania-Verlag.

Cita Chicago (17th ed.)

Klaus, Georg. Was Ist - Was Soll. Leipzig: Urania-Verlag, 1968.

Cita MLA (8th ed.)

Klaus, Georg. Was Ist - Was Soll. Urania-Verlag, 1968.