In this paper we carry the construction of equilogical spaces into an arbitrary category X topological over Set, introducing the category X-Equ of equilogical objects. Similar to what is done for the category Top of topological spaces and continuous functions, we study some features of the new category as (co)completeness and regular (co-)well-poweredness, as well as the fact that, under some conditions, it is a quasitopos. We achieve these various properties of the category X-Equ by representing it as a category of partial equilogical objects, as a reflective subcategory of the exact completion X ex , and as the regular completion X reg . We finish with examples in the particular cases, amongst others, of ordered, metric, and approach spaces, which can all be described using the (T, V)-Cat setting.
IntroductionAs a solution to remedy the problem of non-existence of general exponentials in Top, Scott presents first in [Sco96], and later with his co-authors Bauer and Birkedal in [BBS04], the category Equ of equilogical spaces. Formed by equipping topological T 0 -spaces with arbitrary equivalence relations, Equ contains Top 0 (T 0 -spaces and continuous functions) as a full subcategory and it is cartesian closed. This fact is directly proven by showing an equivalence with the category PEqu of partial equilogical spaces, which is formed by equipping algebraic lattices with partial (not necessarily reflexive) equivalence relations. Also in [BBS04], equilogical spaces are presented as modest sets of assemblies over algebraic lattices, offering a model for dependent type theory. Contributing to the study of Equ, a more general categorical framework, explaining why such (sub)categories are (locally) cartesian closed, was presented in [BCRS98, CR00, Ros99]. It turned out that Equ is related to the free exact completion (Top 0 ) ex of Top 0 [Car95, CM82, CV98]. By the same token, suppressing the T 0 -separation condition on the topological spaces, the category Equ is a full reflective subcategory of the exact completion Top ex of Top. More, the reflector preserves products and special pullbacks, from where it is concluded in [BCRS98] that Equ is locally cartesian closed, since Top ex is so [BCRS98, Theorem 4.1]. It is shown in [Ros98] that Equ can be presented as the free regular completion of Top [Car95, CV98], and [Men00] provides conditions for such regular completions to be quasitoposes.