Determinisation of Relational Substitutions in Ordered Categories with Domain

We present two different relational generalisations of substitutions, show that they both produce locally ordered categories with domain, and then develop the single-morphism “determiniser” concept that relies only on this framework, while still corresponding to conventional two-morphism unification in both examples. Central to this development is the determinacy concept of “characterisation by domain” introduced by Desharnais and Möller for Kleene algebras with domain; this is here applied in the weakest possible setting.