Published online by Cambridge University Press: 20 November 2018
Completions of categories were studied by Lambek in [3], using the contravariant Horn functor to embed a small category C into the functor category (C*, S), where C* is the opposite category of C, and S is the category of sets. Three completions of C were considered; the completion (C*, S), the full subcategory (C*, C)inf⊆(C*, S) whose objects consist of all inf-preserving functors, and the full sub-category B⊆(C*, S)inf consisting of all subobjects of products of representable functors of the form HomC(—, C), C an object of C.