Ideal quotients of $n$-exact categories

Abstract

In this paper, we extend the notion of a removable subcategory to $n$-exact categories, and prove that an ideal quotient by a subcategory of projective-injectives inherits an $n$-exact structure from the original category if and only if the subcategory is removable. In the Frobenius case, the quotient remains Frobenius, and the stable $(n+2)$-angulated categories are equivalent. We give a sufficient condition for a subcategory of projective-injectives to be removable. We also show that the ideal quotient construction is compatible with cluster tilting. Finally, we apply the construction to $2$-cluster tilting subcategories of the category of ACM bundles on a Geigle--Lenzing projective plane, obtaining quotients for both natural and relative $2$-exact structures.