How much work would be involved in order to make the interface for substitution be the same for Maude and Java? In some sense, that is one of the goals of the unified builtins branch, that the same definition be compilable with both backends. I am willing to let this slip if we have to as long as everything that works now in master continues to work and is tested, but I want to at least know what work is entailed before I make that decision.