Differential Algebras in Codifferential Categories

Abstract: Differential categories were introduced by Blute, Cockett, and Seely as categorical models of differential linear logic and have since lead to abstract formulations of many notions involving differentiation such as the directional derivative, differential forms, smooth manifolds, De Rham cohomology, etc. In this paper we study the generalization of differential algebras to the context of differential categories by introducing $\mathsf{T}$-differential algebras, which can be seen as special cases of Blute, Lucyshyn-Wright, and O'Neill's notion of $\mathsf{T}$-derivations. As such, $\mathsf{T}$-differential algebras are axiomatized by the chain rule and as a consequence we obtain both the higher-order Leibniz rule and the Fa`a di Bruno formula for the higher-order chain rule. We also construct both free and cofree $\mathsf{T}$-differential algebras for suitable codifferential categories and discuss power series of $\mathsf{T}$-algebras.