The vertical line was said by Sejong the Great of Joseon to represent man as a mediator between yin (represented by ㅡ (eu, “eu”)) and yang ㆍ (ㆍ, “arae a”). Unrelated to Latin letter I, which is from Phoenician letter 𐤉 (yod) through Greek letter Ι (iota) and Etruscan letter 𐌉.
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