The Nanbokucho-Seijun-ron is a debate on which of the Imperial Courts, Southern or Northern, was the legitimate dynasty during the Nanbokucho period in Japan ("jun" is the same as "uruu" and means "not legitimate but also not fake").
南北朝正閏論（なんぼくちょうせいじゅんろん）とは日本の南北朝時代(日本)において南北のどちらが正統とするかの論争（閏はうるうと同じで「正統ではないが偽物ではない」の意）。