Forgetting

When “this state provably no longer contains X” is a designable property of a system that still works: one object grading how thoroughly a state forgets, what keeping the system working costs that grade, and where robust forgetting stops being purchasable at all.

The systems here are small grown worlds. A state is a positive integer, a move multiplies it by a member of that state's menu — the moves the state admits — and a route is the sequence of moves from the seed state 1, its product being the state it ends at. A world is read at a temperature β: a move m is taken with probability proportional to mβ, normalized by the state's normalizer, the sum of mβ over its menu. A route's probability is then the product of its moves' weights divided by the product of the normalizers it passed through — and since the moves' product is the endpoint, two routes reaching one endpoint differ only in those interior normalizers. Everything about which route was taken lives in what the intermediate states could have done otherwise.

Three worlds carry the census. The depth column takes the constant menu {2, 3} at every state; plain breadth takes the squarefree moves 2..30 coprime to the state; and the tuned amnesiac is a hand-built world — menu 1 → {2, 3}, 2 → {3, 5, 15}, 3 → {2, 10} — whose menus were solved to make one endpoint's routes equiprobable at a named temperature (the one-way design). A world free to reuse a prime it already holds recycles; one every move of which is coprime to the state it acts on cannot.

The certificate's data is three things and a family. A forgotten datum X, any function of history — the route itself, the first move, the multiset of moves. A state map Φ, carrying a history to the still-working present. The weight family, here the temperatures. The fiber of a state is the set of histories Φ sends to it, and the posterior of X there is its conditional distribution on that fiber. What a state keeps is what Φ keeps — the dated endpoint, the value reached together with the number of moves, or the age alone.

The certificate

The four grades and their two witnesses rule

A certificate for X at Φ is a witness at one of four grades, increasing in strength. R, readable: X is a function of Φ, and there is no certificate. P, possibilistic: every fiber meets at least two X-classes, so X is not recoverable as a value; the strongest witness for it is a state-side factoring, a presented split of the history space into X and a remainder with Φ constant in the X slot, which needs no weight at all. T, tuned-flat: at one named temperature the posterior of X is uniform on every fiber's consistent values. S, robust-flat: uniform at every weight in the family. Flatness is fiber-uniformity — maximum entropy behind what the living state logically pins, and never posterior = prior, since a grower's state is its present and so always informs its past possibilistically. It upgrades to posterior = prior for every prior exactly where the split carries the WEIGHTS with it, which is the inheritance route below.

Grade S is bought two ways, and the two forgetting specimens here sit there by different routes — one lemma apart, not one construction apart. Inheritance: where the history space splits as X against a remainder, with X's prior weight-free and Φ reading only the remainder, the posterior of X equals its prior at every state and every weight, with no tuning. Destination universality is grade S by that route: the adapted reader's state is a function of its metabolism and never of its data, which is the factoring. Weight-side symmetry: where the multiset of interior normalizers agrees along every route of a fiber, the route posterior is uniform at every β — route weight is proportional to the product of the reciprocals of those normalizers, and equal multisets have equal products. The depth column is grade S by that route, every normalizer in it being the same polynomial. A third lemma collapses the obvious alternative to a witness: a quotient through which Φ factors, each of whose classes meets every X-class, exists if and only if every Φ-fiber meets every X-class. So “factors through a quotient killing X” is extensionally the FULL-SPREAD case of the possibilistic grade — every fiber meeting every class rather than merely two — and a split witness adds provenance rather than extension.

Scope. The three lemmas proved, scope-free. The grading is an observation exhaustive at the census scope — 406 fibers over the three worlds read to ages 2, 5 and 3 across β ∈ {1, 2, 3}, exact in rationals throughout — and the four grades land whole, with zero fibers they cannot express. The tables read R 3 and T 2 in the tuned world, R 10 and S 10 in the depth column, R 18 and P 363 in breadth. The destination-universality row enters by inheritance together with the factoring measured on the reader side, which holds under every loss that reads only what the reader has committed to and fails outside that family.

verifier: explore_forgetting_certificate.py

The two clauses are independent observation

A certificate carries a structural clause — is there a witness? — and a measure clause — is the posterior flat? Neither implies the other, and both crossings print. Structural kill without flatness: at all 363 of breadth's multi-route fibers the state factors through the quotient that remembers which moves were made and not the order they came in, so the ORDER is possibilistically dead at every one of them — and the posterior still reads that order through the normalizers at β = 1. Flatness without any structural witness: the tuned world's endpoint 6 at age 2 is flat at β = 1 with the witness absent, which is the signature of tuning — it buys one temperature and no more, and the census separates tuned from structural flatness by inspection. What a world forgets is also fiber-local: that same tuned world hides the ORDER at endpoint 6 and hides the move SET at endpoint 30 ({2, 15} against {3, 10}, each admitting exactly one order).

Scope. Exhaustive at the census scope above. The crossing in the remaining direction — robust flatness with no witness — occurs at no fiber here, and whether it can occur at all is the obstruction the coprimality dichotomy settles.

verifier: explore_forgetting_certificate.py

The count leak rule

A certificate for X does not descend to functions of X. Take the depth column, which is route-uniform at every temperature with the weight-side witness present — perfect symmetry, the strongest grade there is. The posterior of the FIRST MOVE at the endpoint 2a3b is nonetheless exactly (a/(a+b), b/(a+b)) — independent of β, and a leak. Route-uniformity does not coarsen to feature-uniformity, because a uniform posterior counted over unequal coarse classes is not uniform. Two leak channels now stand named: the WEIGHT leak, where the measure itself is asymmetric, and the COUNT leak, where only the geometry of the fiber is. Every coarsening needs its own flatness clause.

Scope. The a/(a+b) law proved for the two-move constant menu — equal route weights with binomial fiber counting — and verified at every mixed fiber to age 5; other menus were not scanned. The naming of the two channels is an observation.

verifier: explore_forgetting_certificate.py

Forgetting while the system still works

A still-working system must RETAIN a required function g of its history while certifying that it no longer holds X. Φ computes g exactly when g factors through Φ — equivalently, when Φ's partition of the history space refines g's — so the admissible state maps are exactly the interval from g to the partition into single histories, and the question is whether that interval holds a partition that is spread (every block meets at least two X-classes) and flat. It decomposes fiber by fiber, and the price of a cure is the number of blocks it takes, summed over fibers. Where X is a function of g there is nothing to design: the state is readable.

Refinement never cures, coarsening exposes rule

Two-class conservation. On a g-fiber carrying exactly two X-classes, of masses m₁ and m₂, every spread block holds both classes and flatness forces their two masses equal inside each block; summing over blocks gives m₁ = m₂. So a two-class fiber is curable only where Φ = g is already flat: refinement never cures a two-class leak. The count leak is therefore not merely undescended but UNREMOVABLE while the dated endpoint is retained — deleting a record's attribute while keeping the record runs into a parity-style obstruction that no state design crosses.

The numerator effect. Retention is not monotone the way admissibility is. Conditioning on a dated endpoint cancels the move weights in the numerator, the moves' product being the endpoint itself; conditioning on the AGE alone surfaces them. In the depth column the posterior of first move 2 at an age fiber is exactly 3β/(2β + 3β) — 3/5 at β = 1 — a strict majority at every temperature, and a mass majority is partition-free, so every age fiber leaks whatever state map is built over it. A coarser retained function admits MORE state maps and certifies FEWER: retaining less exposes more.

Scope. Two-class conservation proved. The numerator effect's mechanism is proved and its instances measured at scope: in the depth column with the dated endpoint retained and X the first move, every fiber whose two exponents differ leaks (8 of 20), the equal-exponent ones cure at price 1 and the pure powers are readable, while coarsening to the age alone converts route-uniform fibers into majority-readable ones — the same reversal holding in the tuned world. Where the majority test passes and the individual weight ties a cure would need do exist, no cure assembles at ages 2 or 3 either, so the effect is not a majority artifact.

verifier: explore_working_amnesiac.py

The no-majority criterion criterion

On a uniform-weight g-fiber whose X-class counts are c₁ ≥ ⋯ ≥ cr totalling N, a spread flat partition exists if and only if c₁ ≤ Nc₁ — if and only if no class holds a strict majority. Necessity survives the weighted case as a MASS-majority test, which is partition-free and therefore runs at any fiber size, however far past exhaustive search. Sufficiency is exact subset-mass matching and is NOT claimed weighted, and the distance between the two is where the real price sits: with unequal weights, all 118 searchable non-majority breadth fibers fail to cure. In uniform-weight fibers necessity IS sufficiency; the gap between them is exactly the exact-subset-sum structure of the weight family.

Scope. Proved at uniform-weight scope, and cross-validated against exhaustive partition search — capped at 8 routes per fiber — on all 49 uniform fibers inside that cap, with zero mismatches. The matching-gap count is an observation at the census scope above.

verifier: explore_working_amnesiac.py

The strict amnesiac and the tie desert observation

What the three laws price is curability; what they leave open is whether refinement ever STRICTLY beats the coarsest working state. It does, rarely, and cheaply. In the depth column with the dated endpoint retained and X the first TWO moves, five fibers cure STRICTLY: the coarsest working state Φ = g leaks, and a refinement of it is spread and flat at every temperature. The specimen is class counts (2, 1, 1) with baseline posterior (½, ¼, ¼), cured at price 2 by pairing the two singletons. Partition design alone buys a robust certificate the coarse state does not have. But it is confined to worlds carrying exact weight ties, and plain breadth is a TIE DESERT: across all 363 of its multi-route fibers the interior-normalizer product is INJECTIVE — not one pair of routes carries equal products at β = 1, so no pair can tie across all temperatures at once, and no working state hides the route anywhere in it. For X the first move, of the 291 fibers inside the search cap 173 die by mass majority and 118 pass necessity but admit no exact-tie partition, and none cures. Partition design never manufactures the exact ties working amnesia needs; a symmetry or a tuning has to supply them.

Scope. Exhaustive at the census scope above, exact in rationals, the partition search capped at 8 routes per fiber. The 72 breadth fibers above that cap carry no all-temperature mass majority — the partition-free test runs at any size — so they stay genuinely open rather than decidably leaking. The tie desert is a scope fact and not a theorem: no argument yet says that breadth normalizer products can never tie.

verifier: explore_working_amnesiac.py

What robust forgetting costs

That leaves the obstruction the certificate opened: does robust flatness FORCE a structural witness? It is a factoriality question about the normalizers. Two routes flat at every temperature means their interior-normalizer PRODUCTS agree as functions of β; a weight-side witness means the two MULTISETS agree. So the question is whether equal products force equal factors — and it settles both ways, on one axis, and the axis is coprimality. A world free to recycle its own primes can close a two-route fiber flat at every temperature with distinct multisets, so robust flatness does not force the witness. In a coprime world no dated multi-route fiber is flat at every temperature at any age, so there the question is vacuously yes. Both halves, and the dichotomy they make, are the one-way design. That leaves how WIDE the recycling door is, which is a question about the normalizers alone.

The normalizer semiring is not factorial observation

Read a menu as a Dirichlet polynomial, the sum of mβ over its members. A route's weight is then set by a product of such polynomials, and two routes collide when two products agree identically in β. Collisions are generic rather than exotic: 4849 colliding pairs, falling into 4487 classes by the product they share. Measured directly, one scaling family accounts for 4369 of them: writing ZA for the polynomial of a menu A, and cA for A with every member multiplied by c, they are the instances of ZA·ZcB = ZcA·ZB. Of the 480 non-scaling pairs, 6 involve a single prime, where every menu's polynomial is a polynomial in one variable and factorization already fails to be unique — a factor carrying a negative coefficient cannot itself be a menu, so the remaining factors regroup around it two ways — and 474 involve at least two primes, such as {2}, {3, 6} against {3}, {2, 4}, both products 6β + 12β. Non-unique factorization is the generic state of this semiring, not a cyclotomic curiosity. What limits the door is therefore not the algebra but REALIZATION — whether menus carrying those polynomials assemble into an actual world — and realization's teeth are exactly one degeneracy: the unrealized collisions coincide precisely with the all-singleton ones, 44 of 44, where the four singleton menus of such a pair force equal move products, hence equal leading moves, hence a conflict at the first state. Everything with a non-singleton menu realizes, 4805 of 4849.

Scope. Exhaustive at the collision census's own scope — menus drawn from {2..16} ∪ {32} of size at most 3, with realization seeds up to 8. The singleton direction is proved, over all orders. The same scan cross-checks the coprime half of the dichotomy from outside its proof: zero coprime realizations across all 4849 collisions, against 4805 realizations for worlds free to recycle.

verifier: explore_rogue_world.py

Retention is what prices the certificate. Two-class conservation freezes the count leak, the no-majority criterion prices what is left, and the numerator effect shows that a certificate is not monotone in what is kept — a system holding less of its own history does not thereby forget more of it. And the boundary of robust forgetting is not age but prime recycling: a world whose menus never reuse its own primes cannot help writing its history into its weights. Read as a deletion guarantee — a record removed under a certificate rather than under a retraining story — the price line is that certified forgetting costs prime recycling, and that certifying the erasure of a record never certifies the erasure of its attributes.