Projectivity and flatness over the graded ring of semi-coinvariants
Algebra and discrete mathematics, Tome 10 (2010) no. 1, pp. 42-56
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Let $k$ be a field, $C$ a bialgebra with bijective antipode, $A$ a right $C$-comodule algebra, $G$ any subgroup of the monoid of grouplike elements of $C$. We give necessary and sufficient conditions for the projectivity and flatness over the graded ring of semi-coinvariants of $A$. When $A$ and $C$ are commutative and $G$ is any subgroup of the monoid of grouplike elements of the coring $A\otimes C$, we prove similar results for the graded ring of conormalizing elements of $A$.
@article{ADM_2010_10_1_a4,
author = {T. Gu\'ed\'enon},
title = {Projectivity and flatness over the graded ring of semi-coinvariants},
journal = {Algebra and discrete mathematics},
pages = {42--56},
publisher = {mathdoc},
volume = {10},
number = {1},
year = {2010},
language = {en},
url = {http://geodesic.mathdoc.fr/item/ADM_2010_10_1_a4/}
}
T. Guédénon. Projectivity and flatness over the graded ring of semi-coinvariants. Algebra and discrete mathematics, Tome 10 (2010) no. 1, pp. 42-56. http://geodesic.mathdoc.fr/item/ADM_2010_10_1_a4/