Rings Defined by Extensions

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:

• Invariants by group
• Yoneda Algebra

2010 Mathematics Subject Classification:

• Primary 16E30, 18G15
• Secondary 16S37

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.