The poster of March 1960 South Korean presidential election. Note that the surname Lee (hanja: 李, written as "이" in South Korea today) of Syngman Rhee and Lee Ki-poong were still printed as "리".
Initial sound rule (Korean: 두음법칙; Hanja: 頭音法則; RR: dueum beopchik ) is series of changes to hangul, the writing system for the Korean language, made in South Korea to better reflect modern Korean phonology. The changes affect syllable-initial ㄹ r and ㄴ n sounds in Sino-Korean vocabulary under certain conditions. North Korea orthography does not recognize this rule, making it one of a number of North–South differences in the Korean language.