Sweeney 1973, 322–324쪽. Sweeney, James Ross (1973). “Innocent III, Hungary and the Bulgarian Coronation: A Study in Medieval Papal Diplomacy”. 《Church History》 42 (3): 320–334. doi:10.2307/3164389. JSTOR3164389. S2CID162901328.
Sweeney 1973, 322–324쪽. Sweeney, James Ross (1973). “Innocent III, Hungary and the Bulgarian Coronation: A Study in Medieval Papal Diplomacy”. 《Church History》 42 (3): 320–334. doi:10.2307/3164389. JSTOR3164389. S2CID162901328.
Sweeney 1973, 322–324쪽. Sweeney, James Ross (1973). “Innocent III, Hungary and the Bulgarian Coronation: A Study in Medieval Papal Diplomacy”. 《Church History》 42 (3): 320–334. doi:10.2307/3164389. JSTOR3164389. S2CID162901328.
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이 용어는 헨드릭 W. 오네소르게가 이 문제에 대한 첫 번째 주요 논문에서 소개했다. Ohnsorge 1947 Ohnsorge, Werner (1947). 《Das Zweikaiserproblem im früheren Mittelalter. Die Bedeutung des byzantinischen Reiches für die Entwicklung der Staatsidee in Europa》 (독일어). Hildesheim: A. Lax. OCLC302172.
Geanakoplos 1959, 140f쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.
Geanakoplos 1959, 189f쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.
Geanakoplos 1959, 258–264쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.
Geanakoplos 1959, 264–275쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.
Geanakoplos 1959, 286–290쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.
Geanakoplos 1959, 341쪽. Geanakoplos, Deno John (1959). 《Emperor Michael Palaeologus and the West, 1258–1282: A Study in Byzantine-Latin Relations》. Cambridge, Massachusetts: Harvard University Press. OCLC1011763434.