Let (F(R), Cot(R)) be a cotorsion theory, Such that F(R) is the class of flat Rmodules and Cot(R) the cotorsion modules. Why this is true that, For $ N\in Cot(R) $, $ \text{Ext}_{F(R)}^i(M, N)\cong \text{Ext}_R^i(M, N) $.
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