Three variations on the linear independence of grouplikes in a coalgebra
arXiv:2009.10970
Abstract
The grouplike elements of a coalgebra over a field are known to be linearly independent over said field. Here we prove three variants of this result. One is a generalization to coalgebras over a commutative ring (in which case the linear independence has to be replaced by a weaker statement). Another is a stronger statement that holds (un-der stronger assumptions) in a commutative bialgebra. The last variant is a linear independence result for characters (as opposed to grouplike elements) of a bialgebra.
60 pages. v5 adds Sections 4.4 and 4.5 with counterexamples to two natural questions (found by GPT-5.5). Also, various minor errors fixed