Koszulity of algebras with non-pure resolutions
  We discuss certain homological properties of graded algebras whose trivial modules admit non-pure resolutions. Such algebras include both of Artin-Schelter regular algebras of types (12221) and (13431). Under certain conditions, a module with non-pure resolution is decomposed to form an extension by two modules with pure resolutions. 
Di-Ming Lu and Jun-Ru Si