Quadratic Algebras with Ext Algebras Generated in Two Degrees
نویسندگان
چکیده
Green and Marcos [3] call a graded k-algebra δ-Koszul if the corresponding Yoneda algebra Ext(k, k) is finitely generated and Ext(k, k) is zero unless j = δ(i) for some function δ : N→ N. For any integer m ≥ 3 we exhibit a non-commutative quadratic δ-Koszul algebra for which the Yoneda algebra is generated in degrees (1, 1) and (m,m+ 1). These examples answer a question of Green and Marcos. These algebras are not Koszul but are m-Koszul (in the sense of Backelin).
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