Closure operators in the categories of modules. Part III (Operations in $\mathbb{CO}$ and their properties)

This article is a continuation of the works [1] and [2] (Part I and Part II) and contains some results on the family $\mathbb{CO}$ of all closure operators of a`module category $R$-Mod. The principal operations in $\mathbb{CO}$ (meet, join, product, coproduct) are studied and their properties are elucidated. Also the question on the preservation of types of closure operators with respect to these operations is investigated.