Nakayama closures, interior operations, and core-hull duality – with applications to tight closure theory

Abstract

Exploiting the interior-closure duality developed by Epstein and R.G. [10], we show that for the class of Matlis dualizable modules M over a Noetherian local ring, when cl is a Nakayama closure and i its dual interior, there is a duality between cl-reductions and i-expansions that leads to a duality between the cl-core of modules in M and the i-hull of modules in M∨. We further show that many algebra and module closures and interiors are Nakayama and describe a method to compute the interior of ideals using closures and colons. We use our methods to give a unified proof of the equivalence of F-rationality with F-regularity, and of F-injectivity with F-purity, in the complete Gorenstein local case. Additionally, we give a new characterization of the finitistic tight closure test ideal in terms of maps from R1/pe. Moreover, we show that the liftable integral spread of a module exists.