Ebrey & Walthall 2014Lỗi harv: không có mục tiêu: CITEREFEbreyWalthall2014 (trợ giúp), [1], tr. 171, tại Google Books: Liao forces invaded Goryeo territory in 993. Instead of pushing for total victory, the Khitans negotiated a peace that forced Goryeo to adopt the Liao calendar and end tributary relations with Song (a violation of King Taejo's testamentary injunction never to make peace with the Khitan)."