Yu Gyeongno, Magistrate of Hwangnyeo County, Sent a Letter Labeled on the Outside as to the Fourth Minister (四宰). At First I Doubted It and Would Not Take It, but on Opening It I Found It Was Truly a Letter Sent to Me. In Jest I Composed a Quatrain and Respectfully Sent It (黃驪縣宰柳卿老寄書。標籤爲四宰。初疑不受。及發見。實寄予書也。戱以一絶奉寄。)黃驪縣宰柳卿老寄書。標籤爲四宰。初疑不受。及發見。實寄予書也。戱以一絶奉寄。

Dongguk Isangguk Jip (Collected Works of Minister Yi of the Eastern Country) Latter Collection, Book 2 The collected writings of Yi Gyubo of Goryeo, gathered and cut in woodblock by his son Yi Ham in 1241 and revised and enlarged by his grandson Yi Ikbae in 1251. It holds poems and rhapsodies, memorials and reports sent up to the king, records written for temples and pagodas, stele and tomb inscriptions, letters and prefaces, and the state letters that passed to and from the Mongols during the invasions. The Lay of King Dongmyeong, which sings the founder of Goguryeo, stands in volume 3 of the first collection, and the daily life of a man who called himself the White Cloud Layman — with his wine, his zither and his verse — fills the later collection. The book closes with the last poem he wrote as his eyes failed and he laid down the brush, and with the dirge and tomb inscription others made for him after his death.