APA (7th ed.) Zitazioa
United Nations Publications. United Nations Postage Stamps.
Chicago Style (17th ed.) Zitazioa
United Nations Publications. United Nations Postage Stamps.
MLA (9th ed.) Zitazioa
United Nations Publications. United Nations Postage Stamps.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.