Abstract
In this article, we study subrings of the Ext-algebra of a graded module over a graded ring R. We show these subrings can be defined by equivalence relations on exact sequences over the ring. In particular, the shriek ring, R !, and the even part of an Ext-algebra of a d-Koszul algebra can be defined by equivalence relations on exact sequences.
Key Words:
2010 Mathematics Subject Classification:
ACKNOWLEDGMENT
The first author was supported by grants from CAPES, the second author was partially supported by a grant from the NSA, and the third author was partially supported by grants from CAPES, Cnpq, and Fapesp.
Notes
Communicated by S. Sehgal.