Abstract 1. Introduction 2. Review and proposal 3. Asymmetries in n-insertion 3.1. Asymmetry of n-insertion before /y/ and before /y/ and before /i/ 3.2. Asymmetry between Pure-Korean and Sino-Korean 4. OT analysis for y-devocalization and residual problems 4.1. Presence of y-devocalization 4.2. Absence of y-devocalization 5. Conclusion References