Relative syzygy modules are important research objects of relative homological algebra.In this paper, we will give some equivalent conditions of extension closure,which is the full subcategory consisting of all syzygy modules respect to a projective generator.Some classical results have been extended and strengthened.% 相对合冲模是相对同调代数中重要的研究对象，文中给出了相对于一个投射生成子的合冲模类扩张封闭的一些等价条件，部分结果推广和加强了关于经典的合冲模的相关结论。
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