CLOSURE MATHEMATICS AND THE CONSTRUCTION OF WORLDS Paper II Closure Mathematics Future-Sufficient Representation, Partial Worlds, Defect, Reclosure, and the Algebra of Reduced Description

This paper is the second installment in the six-paper series Closure Mathematics and the Construction of Worlds. Paper I compared three developing programs—Closure Mathematics, Ontological Phase Mathematics, and Ontological Mathematics—with the historical maturation of calculus and Clifford/geometric algebra. Its central conclusion was methodological: a fertile foundational seed is not yet a mature mathematical field. A mathematical program matures when its primitives stabilize, its definitions become transportable, its theorems accumulate, its relations to neighboring theories are made explicit, and its claims survive disciplined comparison with established mathematics. Paper II takes that conclusion seriously. It narrows the focus to the part of the larger archive that is already closest to theorem-generating form: Closure Mathematics as a theory of reduced description, target-relative sufficiency, future relevance, quantified defect, repair, and representational adaptation. Ontological claims are therefore kept outside the formal core unless a mathematical bridge has been supplied. The six-paper sequence is: 1. Paper I — From Foundational Seed to Mathematical Field. 2. Paper II — Closure Mathematics: Future-Sufficient Representation, Partial Worlds, Defect, Reclosure, and the Algebra of Reduced Description. 3. Paper III — From Closure to Life: Persistence, Reproduction, Heredity, Maintenance, and the Alignment of Biological Individuality. 4. Paper IV — The Organism and Its Operational World: Umwelt, Viability, Biological Normativity, Goal-Directedness, and Minimal Agency. 5. Paper V — From Agency to Cognitive Worldhood: Detached Representation, Memory, Learning, Abstraction, and Persistent World Models. 6. Paper VI — Generative Understanding and Shared Worlds: Inferential Closure, Explanation, Language, Teaching, and Collective Cognition. See abstract for rendered equations Any reduced description forgets distinctions. The central mathematical question is therefore not merely how to compress a state space, but which distinctions may be removed without changing the targets, futures, interventions, or decisions that the representation is required to preserve. This paper develops Closure Mathematics as a target-relative theory of representational adequacy and repair. For a state space and target , target equivalence is defined by with canonical quotient This quotient identifies exactly those distinctions invisible to the specified target. The construction is extended from static sufficiency to future-sufficient representation under dynamics, producing horizon- and target-relative quotients determined by the distinctions that remain relevant to admissible futures. Exact closure is then relaxed quantitatively through a closure defect which measures target variation hidden inside the fibers of a representation. This allows exact closure, approximate closure, and partial closure to be separated formally. Approximate closure concerns the magnitude of residual error; partial closure concerns the restricted scope over which closure holds. When a representation fails, the paper introduces a systematic reclosure problem: determine which missing distinctions must be restored without reconstructing the entire hidden state. For an existing representation , the canonical exact refinement required for target is This motivates minimal restoration, restoration-cost functions, interacting closure operators, saturation, closure memory, interventional closure, operational closure, resource-bounded computational closure, and structural reclosure when an entire representation class becomes inadequate. A finite saturation theorem shows that, under standard finite-poset assumptions, repeated fair application of extensive, monotone, idempotent closure operators converges to the least common fixed point above the initial representation. This distinguishes noncommuting closure operations from genuine hysteresis: order dependence of intermediate paths does not by itself imply multiple endpoints or memory. Two constructive appendices strengthen the theorem program without universalizing it. Appendix E proves finite exact and approximate minimal-restoration results together with a uniform target-perturbation stability bound. Appendix F proves finite-dimensional linear future-sufficient protection, identifies a minimum future-relevance dimension, gives a finite cyclic saturation-depth bound, and formalizes nested-class structural reclosure. The framework is compared explicitly with sufficient statistics, Markov lumpability, bisimulation, Mori–Zwanzig projection, predictive-state representations, causal states, information-bottleneck methods, causal abstraction, and reduced-order modeling. The paper does not claim that these mature theories are instances of a single previously hidden universal theorem. Rather, it proposes a common mathematical architecture for asking four questions across them: The common questions are: What may be forgotten? How does forgetting fail? What must be restored? When must the representation itself change? The resulting core of Closure Mathematics is Keywords: Closure Mathematics; sufficient representation; quotient spaces; partial closure; approximate closure; closure defect; reclosure; future-sufficient state; reduced dynamics; saturation; closure operators; memory; hysteresis; interventional closure; causal abstraction; computational closure; model reduction; structural adaptation.