7eec8274b4846eff3ce9e9b113862039c0551b2f06e262cef0961e1f86a3eb4887ca8d

when v_{P/B}+v_{B/A}<=c 
v_{P/A}= v_{P/B}+v_{B/A} 
책엥 엄밀하게능 안나와잇길랭

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