Klaus, G. (1968). Was ist - was soll. Urania-Verlag.
Chicago-Zitierstil (17. Ausg.)Klaus, Georg. Was Ist - Was Soll. Leipzig: Urania-Verlag, 1968.
MLA-Zitierstil (8. Ausg.)Klaus, Georg. Was Ist - Was Soll. Urania-Verlag, 1968.
Nota: a formatação da citação pode não corresponder 100% ao definido pela respectiva norma.