The phrase of Empress Genmei's imperial edict to the enthronement that says 'the law of the nation's governance legislated as Fukai-no-Joten/ Fukaijoten' cited later by Takashi TAKAHASHI is considered as a historically proofed reference.
史料的根拠としては、後に高橋崇があげた元明天皇の即位詔の「不改常典と立て賜わる食国法」という箇所がある。