Moreover, his "Hokusansho" on court ceremonials, which seems to have been written after he retired, is a valuable historical source that shows the details of ceremonies and regular annual events at court during the Regency period.
また引退後著したと見られる有職故実書『北山抄』は摂関政治期における朝廷の儀式・年中行事の詳細が分かる貴重な史料である。