I have just learned the definition for $Ext_{A}^i(M,N)$ where $M,N$ are $A$-modules. However, in the book Quadratic Algebras by Polishchuk and Positselski they sometimes write $Ext_A^{ij}(M,N)$ (for graded $A,M,N$) and they call $j$ the internal grading but I don't understand what this $j$ does. Could someone help me understand what $Ext_A^{ij}(M,N)$ is?
2026-03-25 17:45:16.1774460716
What is the internal grading of Ext
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