Question: The confucian academy, Dosan Seowan, located in the East Asian country bordered by China to the northwest and Russia to the northeast, was founded by two prominant Confucian scholars, one being known as Yi Yulgok. What was the "pen" name of the other founding scholar?
Sentence (from "Korea"): It is separated from Japan to the east by the Korea Strait and the Sea of Japan (East Sea).
Relevant evidence: No