ABSTRACT
Let C be an indecomposable hereditary K-coalgebra, where K is an algebraically closed field. We prove that every left C-comodule is a direct sum of finite dimensional C-comodules if and only if C is comodule Morita equivalent (see Citation[19]) with a path K-coalgebra , where Q is a pure semisimple locally Dynkin quiver, that is, Q is either a finite quiver whose underlying graph is any of the Dynkin diagrams
,
,
,
,
,
,
, or Q is any of the infinite quivers
,
,
, with
, shown in Sec. 2. In particular, we get in Corollaries 2.5 and 2.6 a K-coalgebra analogue of Gabriel's theorem Citation[11] characterising representation-finite hereditary K-algebras (see also [Citation[6], Sec. VIII.5]).
It is shown in Sec. 3 that if , then the Auslander-Reiten quiver
of the category
of finite dimensional left
comodules has at most four connected components, and
is connected if and only if Q has no sink vertices and
.
ACKNOWLEDGMENT
Partially supported by Polish KBN Grant 2 P0 3A 012 16.