Some hypotheses/informations on comparative Korean linguistics

1. there is no r-l contrast in Korean, Japanese or Chinese: Is this areal? Had it been the same in the past ?

2. It is possible that syncope and lenition has kept changing Korean syllable structures complicated for centuries; then the structure was more like Old Japanese before?

3. Vowel comparison between Korean and Japanese is very complicated for vowel systems has changed a lot in the both sides; the causes are vowel harmony for Korean, and Arisaka law for Japanese.