本文给出并证明了右遗传、右完备环上投射模的对偶模仍然是投射模。
This Paper gives and proves the dual module of a projective module over aright hereditary and right perfect ring is stil projective.
是右半遗传环当且仅当任一右R 模的两个上平坦子模的和上平坦；
R is semihereditary ring if and only if the sum of two coflat submodules of every R module is coflat module;
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