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为了研究ＮＥＭＶＤ、ＮＥＪＤ的完备的推导公理，因此对ＮＥＭＶＤ、ＮＥＪＤ的研究转向寻找一种新的依赖类的研究。本文给出了空值环境下子集依赖的概念（强、弱保持），讨论了强、弱保持下的自反律、传递律的存在条件，在此基础上用图算法证明了它们关于ＮＳＤ强保持是完备的。
In order to study the complete deduction axioms of NEMVD and NEJD, the research on NEMVD and NEJD turned to look for a new class of dependent classes. In this paper, the concepts of subset-dependent (strong and weak hold) in null environment are given. The conditions for the existence of strong and weak preserving reflexive laws and transfer laws are discussed. Based on this, Maintain is complete.