Residuation is the law governing the interplay of Flow and Nucleus.
Residuation appeared first in the derivation as Implication: the greatest Judgement z such that z ∧ x ≤ y. There it governed the relationship between Judgements. Here it governs the relationship between Flow and Nucleus — between transformation and closure.
The question Residuation answers at this level is: “given that I transform by Flow and consolidate by Nucleus, how do these two operations constrain each other?” The answer is a precise algebraic relationship — the closure of a flow and the flow of a closure are related by the same residuation structure that generated Implication from Meet and Join.
This is not a coincidence. Residuation is a deep structural pattern that recurs throughout the derivation: wherever two operations must coexist, their interaction is governed by the same “greatest thing compatible with both” structure. It appeared between Judgements as logic; it appears between Flow and Nucleus as dynamics; it will appear between Evolution and Measurement as physics.