Boundary is a structure: the minimal form stabilizing the division between inside and outside.
Given that Distinction is determined by how it structures the division between relation and non-relation, it cannot not derive a dynamic of structure: Boundary. This is the minimal structural form that formalizes and stabilizes the division between the relational unit and what is outside it.
With Boundary, the relational unit is self-sustaining (through Closure) and bounded (through Boundary). But Boundary is inert — the unit has not engaged it, has not turned its relational capacity upon the boundary itself. What determines the coherence of this bounded unit is its distinction between relation and non-relation, and that distinction has not yet been relationally engaged. This undetermination forces the next phase: Folding.