Cohomology of algebras of semidihedral type. IV.
Cohomology of the triangular algebra and applications. (Cohomologie de l'algèbre triangulaire et applications.)
Complexity and periodicity
Let M be a finitely generated module over an Artin algebra. By considering the lengths of the modules in the minimal projective resolution of M, we obtain the Betti sequence of M. This sequence must be bounded if M is eventually periodic, but the converse fails to hold in general. We give conditions under which it holds, using techniques from Hochschild cohomology. We also provide a result which under certain conditions guarantees the existence of periodic modules. Finally, we study the case when...