必异规则(Obligatory Contour Principle<通常简称:ocpxmlns:通常简称="通常简称">,硬性语音结构原则,必要起伏原则,无双原则,强制性非同值原则,强制曲拱制约条件是一种语音假说,指出(某些)连续相同的显著特点(distinctive feature)都被禁止出现在底层表述(underlying representation)上.必异规则(Obligatory Contour (distinctive feature)都被禁止出现在底层表述(underlying representation)上.