Ikegwuoha, M. C. (1991). Voegelin's philosophical concept of order and history: From a political perspective. Pontificia Universitas Urbaniana.
Chicago-viite (17. p.)Ikegwuoha, Michael Chukwunyelunwa. Voegelin's Philosophical Concept of Order and History: From a Political Perspective. Romae: Pontificia Universitas Urbaniana, 1991.
MLA-viite (8. p.)Ikegwuoha, Michael Chukwunyelunwa. Voegelin's Philosophical Concept of Order and History: From a Political Perspective. Pontificia Universitas Urbaniana, 1991.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.