diff --git a/content/essays/index-period-normal-forms/index.md b/content/essays/index-period-normal-forms/index.md deleted file mode 100644 index 4a89916..0000000 --- a/content/essays/index-period-normal-forms/index.md +++ /dev/null @@ -1,1956 +0,0 @@ ---- -title: "Index-Period Normal Forms for Monoid-Aggregated Recursive Summaries" -subtitle: "Exact Pumping, Canonical Representatives, and Computable Test Families" -date: 2026-05-16 -abstract: > - A monoid-aggregated summary evaluates a finite rooted cop-labeled tree - bottom-up through a finite state set and a finite commutative - child-aggregation monoid. Once the multiplicity observation map and the - monoid are fixed, context equivalence has finite index and is exactly - equality of a finite behavior vector. This note sharpens the resulting - pumping and normal-form theory: the crude pigeonhole bound in the product - monoid is replaced by an exact index–period bound on each behavior type's - child contribution, isolating support, modular, and saturation counting in - the Boolean, cyclic, and threshold families. Combining exact sibling - pumping with a size-minimality argument — no behavior vector may repeat - along a root-to-leaf path — yields a finite universe of normal - representatives, and an external tie-break selects one canonical - representative per class. Worked computations for one-node trees, stars, - unary chains, and split-versus-concentrated examples make the bounds - concrete. -tags: - - research - - research/mathematics - - research/algebra - - research/graph-theory -authors: - - "Levi Neuwirth | /me.html" -no-collapse: true -status: "Working model" -confidence: 80 -evidence: 4 -peer-status: unreviewed -result-shape: positive -history: - - date: 2026-05-16 ---- - -## Purpose and executive diagnosis - -The fixed-resource monoid-aggregated model gives a genuine finite-index -theory, but the first normal-form bound is far too coarse if stated only as a -[pigeonhole](https://en.wikipedia.org/wiki/Pigeonhole_principle) bound in a -huge product monoid. The correct next move is to -analyze, for each behavior type, the cyclic submonoid generated by its child -contribution. This gives an exact index-period pumping rule. - -The result is a more useful theory. Sibling multiplicities reduce by -explicit index–period normal forms; the Boolean, cyclic, and threshold -monoids acquire transparent pumping signatures; fixed-resource equivalence -classes gain finite normal representatives; canonical representatives exist -after a harmless external tie-break; and the example computations become -concrete rather than schematic. - -There is also an important algebraic correction. One should not assume that -every [finite commutative monoid](https://en.wikipedia.org/wiki/Monoid) is a -[semilattice](https://en.wikipedia.org/wiki/Semilattice) of [abelian -groups](https://en.wikipedia.org/wiki/Abelian_group). That -statement holds for special regular/Clifford-type commutative monoids, not -for arbitrary finite commutative monoids. Threshold monoids already contain -[aperiodic](https://en.wikipedia.org/wiki/Aperiodic_semigroup) saturation -behavior that is not group-like. The universal -finite-monoid fact needed here is simpler: for each element $g$ of a finite -monoid, the sequence - -$$ -0,\; g,\; 2g,\; 3g,\; \ldots -$$ - -is ultimately periodic. - -**Main principle.** For fixed resources, the relevant algebra is not a global -decomposition of the whole monoid. It is the index-period decomposition of -the cyclic submonoid generated by each realized child-contribution element. - -## The fixed-resource model, recalled - -This section repeats the definitions needed for the present note. The -conventions are unchanged from the finite-resource foundations note. - -::: {.annotation .annotation--static #def-rooted-tree} -
-Definition 2.1 -Rooted cop-labeled tree -
-
- -A *rooted cop-labeled tree* is a finite rooted unordered tree $T$ with root -$\rho_T$ together with a multiplicity function - -$$ -m_T : V(T) \to \mathbb{N}. -$$ - -Sibling order is not part of the structure. - -
-::: - -::: {.annotation .annotation--static #def-context} -
-Definition 2.2 -Rooted one-hole context -
-
- -A *rooted one-hole context* $K[\square]$ is a finite rooted cop-labeled tree -with one distinguished subtree slot. If $X$ is a rooted cop-labeled tree, then -$K[X]$ is obtained by plugging $X$ into the slot. Contexts compose, and the -empty context is $E[\square] = \square$. - -
-::: - -::: {.annotation .annotation--static #def-resource-datum} -
-Definition 2.3 -Finite resource datum -
-
- -A *finite resource datum* is a tuple - -$$ -\mathcal{R} = (A, \mu, S, M, \oplus, 0_M) -$$ - -where: - -1. $A$ is a finite multiplicity alphabet; -2. $\mu : \mathbb{N} \to A$ is a fixed multiplicity observation map; -3. $S$ is a finite state set; -4. $(M, \oplus, 0_M)$ is a finite commutative monoid. - -
-::: - -::: {.annotation .annotation--static #warn-actual-resources} -
-Warning 2.4 -Actual resources, not just cardinalities -
-
- -For the clean fixed-resource theory, $\mu$ and $(M, \oplus, 0_M)$ are part of -the resource datum. Fixing only $|A|$ would allow infinitely many exact -multiplicity tests by varying $\mu$. Fixing only $|M|$ still leaves only -finitely many monoid structures on a fixed finite set, but the pumping -constants depend on the actual operation. Therefore all sharp statements -below are parametrized by the actual resource datum $\mathcal{R}$. - -
-::: - -::: {.annotation .annotation--static #def-summary} -
-Definition 2.5 -Monoid-aggregated summary -
-
- -A *monoid-aggregated summary* over $\mathcal{R}$ is a pair - -$$ -P = (\alpha_P, f_P) -$$ - -with - -$$ -\alpha_P : S \to M, \qquad f_P : A \times M \to S. -$$ - -It evaluates a rooted tree bottom-up by - -$$ -P(T_v) = f_P\!\left( \mu(m_T(v)),\; \bigoplus_{u \text{ child of } v} \alpha_P(P(T_u)) \right), -$$ - -where the empty sum is $0_M$. The root value is denoted $P(T)$. - -
-::: - -::: {.annotation .annotation--static #def-fixed-class} -
-Definition 2.6 -The fixed-resource class -
-
- -Let $D(\mathcal{R})$ be the finite class of all monoid-aggregated summaries -over $\mathcal{R}$. - -
-::: - -::: {.annotation .annotation--static #lem-cardinality} -
-Lemma 2.7 -Crude cardinality of the summary class -
-
- -The number of syntactic summaries over $\mathcal{R}$ is - -$$ -|D(\mathcal{R})| = |M|^{|S|} \cdot |S|^{|A||M|}, -$$ - -where equality means syntactic equality of pairs $(\alpha, f)$. The number of -extensionally distinct summaries is at most this quantity. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Crude cardinality of the summary class" data-exhibit-type="proof" data-exhibit-caption="Count the choices of α : S → M and f : A × M → S independently."} - -:::: exhibit-body -There are $|M|^{|S|}$ choices of $\alpha : S \to M$ and $|S|^{|A||M|}$ choices -of $f : A \times M \to S$. [□]{.proof-qed} -:::: - -::: - -## Behavior vectors and fixed-resource equivalence - -::: {.annotation .annotation--static #def-behavior-vector} -
-Definition 3.1 -Behavior vector -
-
- -The *$\mathcal{R}$-behavior vector* of a tree $T$ is - -$$ -\beta_{\mathcal{R}}(T) = (P(T))_{P \in D(\mathcal{R})} \in S^{D(\mathcal{R})}. -$$ - -We write - -$$ -B_{\mathcal{R}} := S^{D(\mathcal{R})} -$$ - -for the finite set of *formal* behavior vectors. A vector $b \in -B_{\mathcal{R}}$ is *realizable* if $b = \beta_{\mathcal{R}}(T)$ for some tree -$T$. - -
-::: - -::: {.annotation .annotation--static #def-context-equiv} -
-Definition 3.2 -Fixed-resource context equivalence -
-
- -For rooted cop-labeled trees $X, Y$, define - -$$ -X \sim_{\mathcal{R}} Y -$$ - -if for every rooted one-hole context $K[\square]$ and every summary $P \in -D(\mathcal{R})$, - -$$ -P(K[X]) = P(K[Y]). -$$ - -
-::: - -::: {.annotation .annotation--static #thm-behavior-vector} -
-Theorem 3.3 -Fixed-resource equivalence is behavior-vector equality -
-
- -For all rooted cop-labeled trees $X, Y$, - -$$ -X \sim_{\mathcal{R}} Y \iff \beta_{\mathcal{R}}(X) = \beta_{\mathcal{R}}(Y). -$$ - -Consequently $\sim_{\mathcal{R}}$ has finite index, with at most -$|S|^{|D(\mathcal{R})|}$ classes. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Fixed-resource equivalence is behavior-vector equality" data-exhibit-type="proof" data-exhibit-caption="Single-summary context equivalence is root-state equality; intersect over all summaries."} - -:::: exhibit-body -For a single fixed summary $P$, context equivalence is exactly equality of -root state: if two inserted trees have the same root state, the computation -above the hole is identical; conversely, the empty context detects root-state -inequality. Intersecting over all $P \in D(\mathcal{R})$ gives precisely -equality of all coordinates of $\beta_{\mathcal{R}}$. Since $B_{\mathcal{R}} = -S^{D(\mathcal{R})}$ is finite, the finite-index bound follows. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-behavior-type} -
-Remark 3.4 -Behavior type -
-
- -In this note a *behavior type* means an element of $B_{\mathcal{R}}$, usually -a realizable one. Two trees have the same behavior type exactly when they are -$\sim_{\mathcal{R}}$-equivalent. - -
-::: - -::: {.annotation .annotation--static #cor-congruence} -
-Corollary 3.5 -Fixed-resource congruence -
-
- -If $X \sim_{\mathcal{R}} Y$, then for every rooted one-hole context -$K[\square]$, - -$$ -K[X] \sim_{\mathcal{R}} K[Y]. -$$ - -Equivalently, replacing a subtree by another subtree with the same -$\mathcal{R}$-behavior vector preserves the $\mathcal{R}$-behavior vector of -the whole tree. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Fixed-resource congruence" data-exhibit-type="proof" data-exhibit-caption="The inserted subtree is seen above the hole only through its single root state, which agrees for every summary."} - -:::: exhibit-body -By [Theorem 3.3](#thm-behavior-vector), $X \sim_{\mathcal{R}} Y$ means -$\beta_{\mathcal{R}}(X) = \beta_{\mathcal{R}}(Y)$. In the bottom-up evaluation -of any summary $P \in D(\mathcal{R})$ on $K[X]$ or $K[Y]$, the inserted -subtree is seen above the hole only through the single state $P(X)$ or -$P(Y)$. These states agree for every $P$, so the computation above the hole -agrees for every $P$. Applying [Theorem 3.3](#thm-behavior-vector) again gives -$K[X] \sim_{\mathcal{R}} K[Y]$. [□]{.proof-qed} -:::: - -::: - -## The product contribution monoid - -Sibling pumping is most naturally stated in a product monoid that tracks all -summaries simultaneously. - -::: {.annotation .annotation--static #def-product-monoid} -
-Definition 4.1 -Product monoid -
-
- -Let $M^{D(\mathcal{R})}$ denote the product monoid of $D(\mathcal{R})$ copies -of $M$ — equivalently, the set of functions $D(\mathcal{R}) \to M$ — with -coordinatewise operation, also denoted $\oplus$, and zero element $(0_M)_{P -\in D(\mathcal{R})}$. - -
-::: - -::: {.annotation .annotation--static #def-contribution} -
-Definition 4.2 -Contribution element of a behavior type -
-
- -For a formal behavior vector - -$$ -b = (b_P)_{P \in D(\mathcal{R})} \in B_{\mathcal{R}}, -$$ - -define its *product contribution element* - -$$ -\gamma_b \in M^{D(\mathcal{R})} -$$ - -by - -$$ -(\gamma_b)_P := \alpha_P(b_P). -$$ - -Thus $\gamma_b$ is the simultaneous child contribution made by a child -subtree of behavior type $b$ to every summary $P \in D(\mathcal{R})$. This -definition also makes sense for formal, non-realizable behavior vectors; only -realizable vectors occur as actual child types in trees. - -
-::: - -::: {.annotation .annotation--static #rem-notation} -
-Remark 4.3 -Notation checkpoint -
-
- -The symbols used below are as follows: $B_{\mathcal{R}} = S^{D(\mathcal{R})}$ -is the set of formal behavior vectors; $M^{D(\mathcal{R})}$ is the product -contribution monoid; $\gamma_b \in M^{D(\mathcal{R})}$ is the contribution -element of a behavior type $b$; $\operatorname{ind}(\gamma_b)$ and -$\operatorname{per}(\gamma_b)$ are computed inside $M^{D(\mathcal{R})}$; and -$N_{\mathcal{R}}(b) = \operatorname{ind}(\gamma_b) + -\operatorname{per}(\gamma_b) - 1$ is the exact per-type sibling bound. - -
-::: - -::: {.annotation .annotation--static #lem-aggregate} -
-Lemma 4.4 -Sibling aggregate as a product-monoid sum -
-
- -Let a node have child behavior-type multiplicities - -$$ -(n_b)_{b \in B_{\mathcal{R}}}, -$$ - -with all but finitely many $n_b$ zero. Then the simultaneous child aggregate -seen by all summaries is - -$$ -\Gamma := \bigoplus_{b \in B_{\mathcal{R}}} n_b \gamma_b \in M^{D(\mathcal{R})}. -$$ - -The $P$-coordinate of $\Gamma$ is exactly - -$$ -\bigoplus_{u \text{ child}} \alpha_P(P(T_u)), -$$ - -the aggregate used by $P$ at the parent. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Sibling aggregate as a product-monoid sum" data-exhibit-type="proof" data-exhibit-caption="Group children by behavior vector; each contributes α_P(b_P) in coordinate P."} - -:::: exhibit-body -Group the children according to their behavior vector $b$. For each child $u$ -of type $b$, the $P$-coordinate contribution is $\alpha_P(b_P)$. Summing over -all children and all behavior types gives the stated product-monoid -expression. Coordinate $P$ is exactly the ordinary child aggregate for the -summary $P$. [□]{.proof-qed} -:::: - -::: - -## Index-period decomposition in a finite monoid - -We now isolate the elementary finite-monoid fact used throughout the note. -Additive notation means repeated use of the monoid operation: $ng = g \oplus -\cdots \oplus g$ with $n$ copies, and $0g = 0_N$. - -::: {.annotation .annotation--static #def-index-period} -
-Definition 5.1 -Index and period of an element -
-
- -Let $(N, +, 0_N)$ be a finite monoid and let $g \in N$. The sequence - -$$ -0g,\; 1g,\; 2g,\; 3g,\; \ldots -$$ - -is eventually periodic. Define $\operatorname{ind}_N(g)$ to be the least $i -\geq 0$ for which there exists a $p \geq 1$ such that - -$$ -(n+p)g = ng \quad \text{for all } n \geq i. -$$ - -Given this least index, define $\operatorname{per}_N(g)$ to be the least such -positive period $p$. When $N$ is clear, write simply $\operatorname{ind}(g)$ -and $\operatorname{per}(g)$. This is the least-index-then-least-period -convention; other equivalent conventions are possible, but this one is fixed -throughout the note. - -
-::: - -::: {.annotation .annotation--static #lem-existence} -
-Lemma 5.2 -Existence of index and period -
-
- -For every element $g$ of a finite monoid $N$, $\operatorname{ind}(g)$ and -$\operatorname{per}(g)$ exist. Moreover - -$$ -\operatorname{ind}(g) + \operatorname{per}(g) \leq |N|. -$$ - -Equivalently, the exact contribution bound satisfies -$\operatorname{ind}(g) + \operatorname{per}(g) - 1 \leq |N| - 1$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Existence of index and period" data-exhibit-type="proof" data-exhibit-caption="Pigeonhole on the |N|+1 elements 0g,…,|N|g, then associativity gives eventual periodicity."} - -:::: exhibit-body -Among the $|N|+1$ elements - -$$ -0g,\; 1g,\; \ldots,\; |N|g -$$ - -two are equal, say $ig = jg$ with $0 \leq i < j \leq |N|$. Let $p = j - i$. -Then for every $n \geq i$, write $n = i + r$. Associativity gives - -$$ -(n+p)g = (i + r + p)g = (j + r)g = (i + r)g = ng. -$$ - -Thus eventual periodicity holds with $i + p = j \leq |N|$. The -least-index-then-least-period pair can only improve this sum, so -$\operatorname{ind}(g) + \operatorname{per}(g) \leq |N|$. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #def-canon-reduction} -
-Definition 5.3 -Canonical reduction of a coefficient -
-
- -Let $g \in N$, and put - -$$ -i = \operatorname{ind}(g), \quad p = \operatorname{per}(g). -$$ - -Define - -$$ -\operatorname{red}_g(n) = \begin{cases} n, & n < i, \\ i + ((n-i) \bmod p), & n \geq i. \end{cases} -$$ - -Then $0 \leq \operatorname{red}_g(n) \leq i + p - 1$. - -
-::: - -::: {.annotation .annotation--static #lem-unary-pumping} -
-Lemma 5.4 -Exact unary pumping -
-
- -For every $n \geq 0$, - -$$ -ng = \operatorname{red}_g(n)\, g. -$$ - -Moreover $\operatorname{red}_g(n) \leq n$, and if $n > \operatorname{ind}(g) + -\operatorname{per}(g) - 1$, then $\operatorname{red}_g(n) < n$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Exact unary pumping" data-exhibit-type="proof" data-exhibit-caption="Reduce n modulo the period beyond the index; a strict drop occurs once n exceeds ind+per−1."} - -:::: exhibit-body -If $n < i$, the claim is immediate. If $n \geq i$, write - -$$ -n = i + qp + r -$$ - -with $q \geq 0$ and $0 \leq r < p$. By eventual periodicity in steps of $p$ -beyond $i$, - -$$ -ng = (i + qp + r)g = (i + r)g = \operatorname{red}_g(n)\, g. -$$ - -The inequality $\operatorname{red}_g(n) \leq n$ is clear from the formula. If -$n > i + p - 1$, then $q \geq 1$, hence $\operatorname{red}_g(n) = i + r < n$. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #def-contribution-bound} -
-Definition 5.5 -Contribution bound -
-
- -For $g \in N$, define - -$$ -N(g) := \operatorname{ind}(g) + \operatorname{per}(g) - 1. -$$ - -The exact [pumping lemma](https://en.wikipedia.org/wiki/Pumping_lemma) says -every coefficient of $g$ can be reduced to at -most $N(g)$ without changing the monoid value. - -
-::: - -## Exact sibling pumping - -We now apply the index-period decomposition to behavior-type contributions. - -::: {.annotation .annotation--static #def-sibling-signature} -
-Definition 6.1 -Sibling signature -
-
- -For a behavior type $b \in B_{\mathcal{R}}$, its *sibling signature* is - -$$ -\sigma_{\mathcal{R}}(b) := \bigl(\operatorname{ind}(\gamma_b), \operatorname{per}(\gamma_b)\bigr), -$$ - -computed inside the product monoid $M^{D(\mathcal{R})}$. Its *exact sibling -bound* is - -$$ -N_{\mathcal{R}}(b) := \operatorname{ind}(\gamma_b) + \operatorname{per}(\gamma_b) - 1. -$$ - -A uniform exact sibling bound is - -$$ -N^{\max}_{\mathcal{R}} := \max_{b \in B_{\mathcal{R}}} N_{\mathcal{R}}(b). -$$ - -
-::: - -::: {.annotation .annotation--static #thm-sibling-pumping} -
-Theorem 6.2 -Exact sibling pumping at one node -
-
- -Let a node have child behavior-type multiplicities $(n_b)_{b \in -B_{\mathcal{R}}}$. For each $b$, set - -$$ -n'_b := \operatorname{red}_{\gamma_b}(n_b). -$$ - -Replace the child multiset by one having exactly $n'_b$ children of behavior -type $b$ for every $b$, using any available representatives of those behavior -types. Then the simultaneous child aggregate in $M^{D(\mathcal{R})}$ is -unchanged. Consequently, if the node's observed multiplicity label is -unchanged, then its parent behavior vector is unchanged. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Exact sibling pumping at one node" data-exhibit-type="proof" data-exhibit-caption="Per-type unary pumping leaves each n_b γ_b unchanged, hence the whole product aggregate."} - -:::: exhibit-body -By [Lemma 4.4](#lem-aggregate), the original simultaneous child aggregate is - -$$ -\Gamma = \bigoplus_b n_b \gamma_b. -$$ - -The new aggregate is - -$$ -\Gamma' = \bigoplus_b n'_b \gamma_b. -$$ - -By [Lemma 5.4](#lem-unary-pumping), $n_b \gamma_b = n'_b \gamma_b$ for each -$b$. Therefore $\Gamma = \Gamma'$. Coordinatewise, every summary $P \in -D(\mathcal{R})$ receives the same child aggregate at the node. Since the -observed multiplicity label is also unchanged, every $P$ assigns the same -parent state as before. Hence the whole behavior vector at the node is -unchanged. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #cor-sibling-normal-form} -
-Corollary 6.3 -Exact sibling normal form -
-
- -Every sibling multiset is equivalent, as seen by all summaries in -$D(\mathcal{R})$, to one in which each behavior type $b$ occurs at most - -$$ -N_{\mathcal{R}}(b) = \operatorname{ind}(\gamma_b) + \operatorname{per}(\gamma_b) - 1 -$$ - -times. In particular, the total number of children after exact sibling -normalization is at most - -$$ -C_{\mathcal{R}} := \sum_{b \in B_{\mathcal{R}}} N_{\mathcal{R}}(b) \leq |B_{\mathcal{R}}| \cdot N^{\max}_{\mathcal{R}}. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Exact sibling normal form" data-exhibit-type="proof" data-exhibit-caption="Apply the one-node pumping theorem per behavior type."} - -:::: exhibit-body -Apply [Theorem 6.2](#thm-sibling-pumping) to each behavior type. The -resulting count $n'_b$ satisfies $n'_b \leq N_{\mathcal{R}}(b)$. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-realizable-formal} -
-Remark 6.4 -Realizable versus formal behavior types -
-
- -The bounds may be sharpened by taking $b$ only over realizable behavior -vectors. The present statement uses all formal $b \in B_{\mathcal{R}}$ to -avoid introducing a separate realizability analysis. Note that realizability -of behavior vectors is defined existentially over all trees and is not in -general algorithmically transparent, so the formal-version bounds are also -the practically computable ones. - -
-::: - -## Canonical monoid families - -The index-period form makes the standard monoid families transparent. - -### Boolean semilattices - -::: {.annotation .annotation--static #prop-boolean} -
-Proposition 7.1 -Boolean support pumping -
-
- -Let $M = (\{0, 1\}, \vee, 0)$. Then for $g = 0$, - -$$ -\operatorname{ind}(g) = 0, \quad \operatorname{per}(g) = 1, \quad N(g) = 0, -$$ - -and for $g = 1$, - -$$ -\operatorname{ind}(g) = 1, \quad \operatorname{per}(g) = 1, \quad N(g) = 1. -$$ - -Thus a nonzero child contribution is remembered only by presence or absence. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Boolean support pumping" data-exhibit-type="proof" data-exhibit-caption="g = 0 is periodic from index 0; g = 1 stabilizes at 1 from index 1."} - -:::: exhibit-body -If $g = 0$, then $ng = 0$ for all $n$, so the sequence is periodic from index -$0$ with period $1$. If $g = 1$, then $0g = 0$ and $ng = 1$ for all $n \geq -1$, so the sequence has index $1$ and period $1$. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #cor-boolean-product} -
-Corollary 7.2 -Boolean product bound -
-
- -If $M$ is a finite Boolean semilattice, for example a finite power of $(\{0, -1\}, \vee, 0)$, every element is -[idempotent](https://en.wikipedia.org/wiki/Idempotence). Hence every behavior type has -bound $0$ if its contribution is zero and bound $1$ otherwise. - -
-::: - -### Finite cyclic groups - -::: {.annotation .annotation--static #prop-cyclic} -
-Proposition 7.3 -Cyclic group pumping -
-
- -Let $M = \mathbb{Z}/q\mathbb{Z}$ under addition. For $g \in M$, - -$$ -\operatorname{ind}(g) = 0, \quad \operatorname{per}(g) = \operatorname{ord}(g) = \frac{q}{\gcd(q, g)}, -$$ - -with the convention that $\operatorname{ord}(0) = 1$. Thus - -$$ -N(g) = \operatorname{ord}(g) - 1. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Cyclic group pumping" data-exhibit-type="proof" data-exhibit-caption="ng is periodic from the start with least period the additive order of g."} - -:::: exhibit-body -The sequence $ng$ is periodic from the beginning. Its least positive period -is the [additive order](https://en.wikipedia.org/wiki/Order_(group_theory)) -of $g$ in the [cyclic group](https://en.wikipedia.org/wiki/Cyclic_group). The displayed formula for -the order in $\mathbb{Z}/q\mathbb{Z}$ is standard. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #cor-cyclic-product} -
-Corollary 7.4 -Product of cyclic groups -
-
- -If $M$ is a finite abelian group and $g \in M$, then - -$$ -\operatorname{ind}(g) = 0, \quad \operatorname{per}(g) = \operatorname{ord}(g), \quad N(g) = \operatorname{ord}(g) - 1. -$$ - -For a product element $g = (g_i)$, $\operatorname{ord}(g)$ is the least -common multiple of the coordinate orders. - -
-::: - -### Threshold monoids - -::: {.annotation .annotation--static #def-threshold} -
-Definition 7.5 -Threshold monoid -
-
- -For $T \geq 0$, let - -$$ -\Theta_T := \{0, 1, \ldots, T\} -$$ - -with operation - -$$ -x \oplus y := \min(T, x + y) -$$ - -and identity $0$. - -
-::: - -::: {.annotation .annotation--static #prop-threshold} -
-Proposition 7.6 -Threshold pumping -
-
- -Let $M = \Theta_T$. If $g = 0$, then $\operatorname{ind}(g) = 0$, -$\operatorname{per}(g) = 1$, and $N(g) = 0$. If $1 \leq g \leq T$, then - -$$ -\operatorname{ind}(g) = \lceil T/g \rceil, \quad \operatorname{per}(g) = 1, \quad N(g) = \lceil T/g \rceil. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Threshold pumping" data-exhibit-type="proof" data-exhibit-caption="The sequence climbs until it saturates at T after ⌈T/g⌉ steps, then is constant."} - -:::: exhibit-body -For $g = 0$ the sequence is constantly zero. If $T = 0$, this is the only -case. For $g > 0$, - -$$ -ng = \min(T, ng) -$$ - -in ordinary integer notation. The first $n$ for which $ng$ reaches $T$ is -$\lceil T/g \rceil$. From that index onward the sequence is constantly $T$, -hence the period is $1$. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-aperiodic} -
-Remark 7.7 -Aperiodic saturation -
-
- -Threshold monoids show why arbitrary finite commutative monoids cannot be -treated as semilattices of abelian groups. In $\Theta_2$, the element $1$ has -the sequence $0, 1, 2, 2, 2, \ldots$; this has a genuine preperiod and no -group-like cycle before saturation. - -
-::: - -### Threshold-times-cyclic products - -::: {.annotation .annotation--static #prop-hybrid} -
-Proposition 7.8 -Hybrid threshold-residue pumping -
-
- -Let - -$$ -M = \Theta_T \times \mathbb{Z}/q\mathbb{Z} -$$ - -with coordinatewise operation, and let $g = (g_{\text{thr}}, g_{\text{cyc}})$. -Then - -$$ -\operatorname{ind}(g) = \begin{cases} 0, & g_{\text{thr}} = 0, \\ \lceil T/g_{\text{thr}} \rceil, & g_{\text{thr}} > 0, \end{cases} -$$ - -and - -$$ -\operatorname{per}(g) = \operatorname{ord}(g_{\text{cyc}}). -$$ - -Consequently - -$$ -N(g) = \operatorname{ind}(g) + \operatorname{per}(g) - 1. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Hybrid threshold-residue pumping" data-exhibit-type="proof" data-exhibit-caption="The threshold coordinate fixes the index; the cyclic coordinate fixes the period."} - -:::: exhibit-body -If $g_{\text{thr}} = 0$, the threshold coordinate is constantly $0$ and the -product period is exactly the cyclic order. If $g_{\text{thr}} > 0$, the -threshold coordinate strictly changes until the first index - -$$ -i = \lceil T/g_{\text{thr}} \rceil, -$$ - -at which it reaches $T$ and remains constant. Thus no smaller index can work. -From index $i$ onward, the threshold coordinate contributes period $1$, while -the cyclic coordinate has least period $\operatorname{ord}(g_{\text{cyc}})$. -Therefore the product has least period $\operatorname{ord}(g_{\text{cyc}})$ -from the least possible index $i$. [□]{.proof-qed} -:::: - -::: - -### Product bounds in general - -::: {.annotation .annotation--static #prop-coord-product} -
-Proposition 7.9 -Coordinatewise product bound -
-
- -Let $N = N_1 \times \cdots \times N_r$ be a product of finite monoids and let -$g = (g_1, \ldots, g_r)$. If $i_j = \operatorname{ind}(g_j)$ and $p_j = -\operatorname{per}(g_j)$, then a valid index-period pair for $g$ is - -$$ -i = \max_j i_j, \quad p = \operatorname{lcm}_j p_j. -$$ - -Thus - -$$ -N(g) \leq \max_j i_j + \operatorname{lcm}_j p_j - 1. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Coordinatewise product bound" data-exhibit-type="proof" data-exhibit-caption="Beyond the max index, adding the lcm of periods preserves every coordinate."} - -:::: exhibit-body -For every coordinate $j$, the sequence $n g_j$ is periodic with period $p_j$ -from index $i_j$ onward. Once $n \geq \max_j i_j$, adding $p = -\operatorname{lcm}_j p_j$ preserves every coordinate. Hence it preserves the -product element. [□]{.proof-qed} -:::: - -::: - -## Examples: exact computations - -This section records concrete test families. These are not yet -pursuit-evasion applications; they are calibration examples for the summary -model. - -### One-node trees - -Let $A_n$ be the one-node tree whose root multiplicity is $n$. - -::: {.annotation .annotation--static #prop-one-node} -
-Proposition 8.1 -One-node criterion -
-
- -For fixed $\mathcal{R}$, if - -$$ -\mu(n) = \mu(m), -$$ - -then - -$$ -A_n \sim_{\mathcal{R}} A_m. -$$ - -Conversely, if $\mu(n) \neq \mu(m)$ and $|S| \geq 2$, then $A_n$ and $A_m$ -are separated by some summary in $D(\mathcal{R})$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="One-node criterion" data-exhibit-type="proof" data-exhibit-caption="A one-node tree has empty child aggregate, so its state depends only on μ(n)."} - -:::: exhibit-body -A one-node tree has empty child aggregate. Hence for every $P = (\alpha_P, -f_P)$, - -$$ -P(A_n) = f_P(\mu(n), 0_M). -$$ - -If $\mu(n) = \mu(m)$, these values are equal for all $P$, so [Theorem -3.3](#thm-behavior-vector) gives equivalence. - -If $\mu(n) \neq \mu(m)$ and $|S| \geq 2$, choose two distinct states $s_0, -s_1 \in S$. Define $f$ so that $f(\mu(n), 0_M) = s_0$ and $f(\mu(m), 0_M) = -s_1$, extending $f$ arbitrarily elsewhere. Choose any $\alpha : S \to M$. The -resulting summary separates $A_n$ and $A_m$. [□]{.proof-qed} -:::: - -::: - -### Stars - -Fix a rooted tree $Q$ with behavior vector $b = \beta_{\mathcal{R}}(Q)$. Let -$\mathrm{Star}_n(a; Q)$ be the tree with root observed multiplicity label $a -\in A$ and $n$ children, each isomorphic to $Q$. More precisely, choose any -root multiplicity $r$ with $\mu(r) = a$. - -::: {.annotation .annotation--static #prop-stars} -
-Proposition 8.2 -Star aggregate criterion -
-
- -For fixed $a$ and $Q$, if - -$$ -n \gamma_b = m \gamma_b -$$ - -in the product monoid $M^{D(\mathcal{R})}$, then - -$$ -\mathrm{Star}_n(a; Q) \sim_{\mathcal{R}} \mathrm{Star}_m(a; Q). -$$ - -More generally, the two stars have the same behavior vector exactly when, for -every summary $P \in D(\mathcal{R})$, - -$$ -f_P(a, n \alpha_P(b_P)) = f_P(a, m \alpha_P(b_P)). -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Star aggregate criterion" data-exhibit-type="proof" data-exhibit-caption="Root state is f_P(a, n α_P(b_P)); product-aggregate equality forces coordinatewise equality."} - -:::: exhibit-body -For every summary $P$, the root state is $f_P(a, n \alpha_P(b_P))$ for the -first star and $f_P(a, m \alpha_P(b_P))$ for the second. The coordinatewise -equality displayed in the proposition is therefore exactly behavior-vector -equality. The product-monoid identity $n \gamma_b = m \gamma_b$ implies that -equality, since its $P$-coordinate is precisely - -$$ -n \alpha_P(b_P) = m \alpha_P(b_P) -$$ - -for every $P$. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-aggregate-sufficient} -
-Remark 8.3 -Why aggregate equality is sufficient, not necessary -
-
- -The implication from product-aggregate equality to star equivalence is the -one needed for pumping and normal forms. It is not generally necessary: two -different aggregates may be identified by all root update maps at the -observed label $a$ for the summaries under discussion. In particular examples -one can often force separation by choosing a summary whose update map -distinguishes the two aggregates, but the exact statement is the displayed -coordinatewise criterion. - -
-::: - -::: {.annotation .annotation--static #ex-stars} -
-Example 8.4 -Stars in standard monoids -
-
- -Assume unit contribution $\gamma_b = g$. - -1. Boolean support: all positive $n$ are equivalent; $n = 0$ is separate from - $n > 0$ if $g \neq 0$. -2. Cyclic $\mathbb{Z}/q\mathbb{Z}$: $n$ and $m$ are equivalent exactly modulo - $\operatorname{ord}(g)$. -3. Threshold $\Theta_T$ with $g = 1$: $n$ and $m$ are equivalent iff either - $n = m < T$ or both $n, m \geq T$. - -
-::: - -### Unary chains - -Unary-chain behavior is controlled by finite transformations on behavior -vectors, not directly by the horizontal child-aggregation monoid. - -::: {.annotation .annotation--static #def-unary-map} -
-Definition 8.5 -Unary extension map -
-
- -For each observed multiplicity label $a \in A$, define - -$$ -U_a : B_{\mathcal{R}} \to B_{\mathcal{R}} -$$ - -by declaring $U_a(b)$ to be the behavior vector of a new root with observed -label $a$ and exactly one child of behavior type $b$. Coordinatewise, - -$$ -(U_a(b))_P = f_P(a, \alpha_P(b_P)). -$$ - -
-::: - -::: {.annotation .annotation--static #prop-unary-periodic} -
-Proposition 8.6 -Unary chains are eventually periodic -
-
- -Fix $a \in A$ and $b \in B_{\mathcal{R}}$. The sequence - -$$ -b,\; U_a(b),\; U_a^2(b),\; U_a^3(b),\; \ldots -$$ - -is eventually periodic. In particular, among the first $|B_{\mathcal{R}}| + -1$ terms two are equal. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Unary chains are eventually periodic" data-exhibit-type="proof" data-exhibit-caption="U_a is a self-map of the finite set B_R; every finite-set orbit is eventually periodic."} - -:::: exhibit-body -The map $U_a$ is a self-map of the finite set $B_{\mathcal{R}}$. Every orbit -of a self-map on a finite set is eventually periodic, and the pigeonhole -principle gives a repetition among the first $|B_{\mathcal{R}}| + 1$ terms. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #cor-unary-pumping} -
-Corollary 8.7 -Unary chain pumping -
-
- -Any sufficiently long constant-label unary chain contains a proper subchain -whose deletion preserves the behavior vector at the top of the chain. A crude -bound is $|B_{\mathcal{R}}| + 1$ vertices for a repeated behavior vector. - -
-::: - -::: {.annotation .annotation--static #rem-variable-labels} -
-Remark 8.8 -Variable labels -
-
- -If labels vary along a unary path, one obtains the finite [transformation -semigroup](https://en.wikipedia.org/wiki/Transformation_semigroup) -generated by the maps $U_a$ for $a \in A$: this is the subsemigroup, -under composition, of the finite monoid of all self-maps of $B_{\mathcal{R}}$ -generated by the maps $U_a$. Long labeled unary words can be pumped using -repetitions in this finite transformation semigroup, but the -minimal-representative argument in [Section -9](#global-normal-representatives) gives a simpler global height bound for -entire trees. - -
-::: - -### Split versus concentrated examples - -Let $Q$ be a tree of behavior type $b$. A simple split tree has a root with -two children of type $b$, hence horizontal contribution - -$$ -2 \gamma_b. -$$ - -A concentrated competitor has a root with one child $R$ of behavior type $c$, -where the internal construction of $R$ may have encoded some information that -resembles two copies of $b$ at a lower level. - -::: {.annotation .annotation--static #prop-split-concentrated} -
-Proposition 8.9 -Diagnostic criterion -
-
- -Suppose two trees have the same observed root label $a$. One has child -multiset consisting of two children of behavior type $b$, and the other has -one child of behavior type $c$. Their root behavior vectors are equal exactly -when, for every $P \in D(\mathcal{R})$, - -$$ -f_P(a, 2\alpha_P(b_P)) = f_P(a, \alpha_P(c_P)). -$$ - -Equivalently, equality follows from the stronger aggregate identity - -$$ -2 \gamma_b = \gamma_c -$$ - -in $M^{D(\mathcal{R})}$, but may also occur accidentally because all update -maps in question identify the two aggregates at label $a$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Diagnostic criterion" data-exhibit-type="proof" data-exhibit-caption="Immediate from coordinatewise root evaluation; aggregate equality is sufficient but not necessary."} - -:::: exhibit-body -This is immediate from the coordinatewise evaluation formula at the root. -Aggregate equality is sufficient. It is not necessary for an arbitrary fixed -subfamily of updates because two different aggregates may be mapped to the -same state by every relevant $f_P$ at the label $a$. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-no-converse} -
-Remark 8.10 -No automatic converse from aggregate inequality -
-
- -The stronger aggregate identity $2\gamma_b = \gamma_c$ is a clean sufficient -condition for equality of the two root behavior vectors. Its failure is not, -by itself, a clean separation theorem. The behavior coordinates $b_P, c_P$ of -the child subtrees are fixed properties of those subtrees, indexed by every -$P \in D(\mathcal{R})$. If a particular coordinate $P^*$ witnesses aggregate -inequality in $M^{D(\mathcal{R})}$, the summary $P^*$ itself may still fail to -separate the parents because $f_{P^*}$ may identify the two aggregates. One -cannot remedy this by "switching to a different $f$" while holding the child -contributions fixed: choosing a different summary $P'$ means looking at a -different coordinate $P'$ of the child behavior vectors, with potentially -different aggregate values. Thus separation should be checked by the exact -coordinatewise criterion in [Proposition 8.2](#prop-stars) and [Proposition -8.9](#prop-split-concentrated), not by aggregate inequality alone. This is -precisely why split-versus-concentrated examples are diagnostically -interesting rather than trivial. - -
-::: - -::: {.annotation .annotation--static #rem-family-matters} -
-Remark 8.11 -Why this family matters -
-
- -This is the first family where horizontal aggregation interacts with vertical -recursion. It is a natural bridge to later pursuit-evasion questions about -whether support is split across branches or concentrated inside one branch. - -
-::: - -## Global normal representatives - -Exact sibling pumping bounds branching. To obtain a finite universe of -representatives, one also needs a height bound. The cleanest argument is not a -unary-chain analysis; it is minimality. - -::: {.annotation .annotation--static #def-label-rep} -
-Definition 9.1 -Observed-label representative -
-
- -Choose once and for all a representative integer $r(a) \in \mathbb{N}$ for -each $a \in A$ with $\mu(r(a)) = a$, for every $a$ in the image of $\mu$. No -representative is needed for $a \notin \operatorname{im}(\mu)$, since no -vertex of any tree has observed label $a$. A tree is *label-normalized* if -every vertex with observed label $a$ has actual multiplicity $r(a)$. - -
-::: - -::: {.annotation .annotation--static #lem-label-normalization} -
-Lemma 9.2 -Label normalization preserves behavior -
-
- -Every tree $T$ is $\sim_{\mathcal{R}}$-equivalent to a label-normalized tree -$T^{\ell}$ with the same underlying rooted unordered tree and the same -observed labels. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Label normalization preserves behavior" data-exhibit-type="proof" data-exhibit-caption="Summaries use multiplicities only through μ, so replacing m by r(μ(m)) changes nothing."} - -:::: exhibit-body -Replace each vertex multiplicity $m$ by $r(\mu(m))$. Every summary in -$D(\mathcal{R})$ uses multiplicities only through $\mu$, so every bottom-up -computation is unchanged. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #def-size-minimal} -
-Definition 9.3 -Size-minimal representative -
-
- -A tree $T$ is *size-minimal* for its behavior vector if among all trees $T'$ -with $\beta_{\mathcal{R}}(T') = \beta_{\mathcal{R}}(T)$, the number of -vertices of $T'$ is minimized. It is *normalized size-minimal* if it is also -label-normalized. - -
-::: - -::: {.annotation .annotation--static #lem-minimal-exists} -
-Lemma 9.4 -Size-minimal representatives exist -
-
- -Every realizable behavior vector has a normalized size-minimal -representative. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Size-minimal representatives exist" data-exhibit-type="proof" data-exhibit-caption="Pick a fewest-vertex realizer, then label-normalize it without changing vertex count."} - -:::: exhibit-body -The behavior vector is realizable, so at least one tree realizes it. Among -all realizing trees, choose one with the fewest vertices. Apply [Lemma -9.2](#lem-label-normalization) to normalize labels without changing the -number of vertices or the behavior vector. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #thm-minimal-sibling-bounded} -
-Theorem 9.5 -Minimal representatives are sibling-bounded -
-
- -Let $T$ be a normalized size-minimal representative. At every node $v$ of -$T$, each child behavior type $b$ occurs at most - -$$ -N_{\mathcal{R}}(b) = \operatorname{ind}(\gamma_b) + \operatorname{per}(\gamma_b) - 1 -$$ - -times. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Minimal representatives are sibling-bounded" data-exhibit-type="proof" data-exhibit-caption="An over-full sibling type could be pumped down, contradicting size-minimality."} - -:::: exhibit-body -Suppose some node $v$ has $n_b > N_{\mathcal{R}}(b)$ children of behavior -type $b$. By [Lemma 5.4](#lem-unary-pumping), replacing $n_b$ by -$\operatorname{red}_{\gamma_b}(n_b)$ preserves the contribution of type $b$, -and by the same lemma this reduced number satisfies -$\operatorname{red}_{\gamma_b}(n_b) < n_b$. Delete enough children of type -$b$ to leave exactly $\operatorname{red}_{\gamma_b}(n_b)$ such children, -leaving all other child types unchanged. The simultaneous child aggregate at -$v$ is unchanged, so the behavior vector of the subtree rooted at $v$ is -unchanged. By [Corollary 3.5](#cor-congruence), the behavior vector of the -whole tree is unchanged. But the number of vertices strictly decreases, -contradicting size-minimality. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #thm-no-repeat} -
-Theorem 9.6 -Minimal representatives have no repeated behavior along a path -
-
- -Let $T$ be a normalized size-minimal representative. No root-to-leaf path of -$T$ contains two distinct vertices $u$ and $v$, with $v$ a proper descendant -of $u$, such that - -$$ -\beta_{\mathcal{R}}(T_u) = \beta_{\mathcal{R}}(T_v). -$$ - -Consequently every root-to-leaf path has at most $|B_{\mathcal{R}}|$ -vertices. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Minimal representatives have no repeated behavior along a path" data-exhibit-type="proof" data-exhibit-caption="A repeated behavior vector lets the upper subtree be replaced by the lower one, shrinking the tree."} - -:::: exhibit-body -Suppose $v$ is a proper descendant of $u$ and the rooted subtrees $T_u$ and -$T_v$ have the same behavior vector. Replace the subtree $T_u$ by the proper -descendant subtree $T_v$. Since the two subtrees are -$\sim_{\mathcal{R}}$-equivalent by [Theorem 3.3](#thm-behavior-vector), -[Corollary 3.5](#cor-congruence) implies that the behavior vector of the -whole tree is unchanged. The replacement strictly decreases the number of -vertices, contradicting size-minimality. Therefore no behavior vector -repeats along a path. Since an actual path encounters only realizable -behavior vectors, every path has at most the number of realizable behavior -vectors, and in particular at most $|B_{\mathcal{R}}|$ vertices. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #def-normal-universe} -
-Definition 9.7 -Normal universe -
-
- -Let $U_{\mathcal{R}}$ be the finite set of all label-normalized rooted -cop-labeled trees satisfying: - -1. every root-to-leaf path has at most $|B_{\mathcal{R}}|$ vertices; -2. at every node, behavior type $b$ occurs among the children at most - $N_{\mathcal{R}}(b)$ times, for every $b \in B_{\mathcal{R}}$. - -
-::: - -::: {.annotation .annotation--static #rem-sharper-universe} -
-Remark 9.8 -Sharper realizable normal universe -
-
- -One may replace $|B_{\mathcal{R}}|$ and the sum over all formal $b \in -B_{\mathcal{R}}$ by the corresponding quantities for realizable behavior -vectors. The formal version is cruder but avoids a separate realizability -computation. Since realizability is defined existentially over all trees and -is not in general algorithmically transparent, the formal version is also the -version most directly usable in computations. - -
-::: - -::: {.annotation .annotation--static #thm-normal-universe} -
-Theorem 9.9 -Finite global normal representatives -
-
- -Every $\sim_{\mathcal{R}}$-equivalence class has a representative in the -finite universe $U_{\mathcal{R}}$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Finite global normal representatives" data-exhibit-type="proof" data-exhibit-caption="A normalized size-minimal representative satisfies both universe constraints; the universe is finite."} - -:::: exhibit-body -Let $b$ be a realizable behavior vector. By [Lemma -9.4](#lem-minimal-exists), choose a normalized size-minimal representative -$T$ realizing $b$. By [Theorem 9.5](#thm-minimal-sibling-bounded), $T$ -satisfies the exact sibling bounds. By [Theorem 9.6](#thm-no-repeat), its -root-to-leaf paths have at most $|B_{\mathcal{R}}|$ vertices. Thus $T \in -U_{\mathcal{R}}$. - -The set $U_{\mathcal{R}}$ is finite because labels come from the finite image -of $\mu$, height is bounded, and at each node the number of children is -bounded by - -$$ -C_{\mathcal{R}} = \sum_{b \in B_{\mathcal{R}}} N_{\mathcal{R}}(b). -$$ - -There are only finitely many finite unordered rooted trees with bounded -height, bounded branching, and labels from a finite alphabet. -[□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #cor-size-bound} -
-Corollary 9.10 -Crude size bound -
-
- -Let - -$$ -H_{\mathcal{R}} := |B_{\mathcal{R}}|, \quad C_{\mathcal{R}} := \sum_{b \in B_{\mathcal{R}}} N_{\mathcal{R}}(b). -$$ - -Then every class has a representative with at most - -$$ -1 + C_{\mathcal{R}} + C_{\mathcal{R}}^2 + \cdots + C_{\mathcal{R}}^{H_{\mathcal{R}} - 1} -$$ - -vertices, with the usual interpretation as $H_{\mathcal{R}}$ when -$C_{\mathcal{R}} = 1$. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Crude size bound" data-exhibit-type="proof" data-exhibit-caption="Sum the geometric series for ≤ H_R levels with branching ≤ C_R."} - -:::: exhibit-body -Here $H_{\mathcal{R}}$ bounds the number of vertices on a root-to-leaf path, -so the tree has at most $H_{\mathcal{R}}$ levels, indexed $0, 1, \ldots, -H_{\mathcal{R}} - 1$. With branching at most $C_{\mathcal{R}}$, level $d$ has -at most $C_{\mathcal{R}}^d$ vertices. Summing over the levels gives the -displayed bound; when $C_{\mathcal{R}} = 1$ the geometric sum has -$H_{\mathcal{R}}$ terms each equal to $1$, giving $H_{\mathcal{R}}$. -[□]{.proof-qed} -:::: - -::: - -## Canonical representatives - -A finite normal universe gives canonical representatives once one imposes an -external tie-break. This is safer than claiming that minimal representatives -are intrinsically unique, which is generally false. - -::: {.annotation .annotation--static #def-external-order} -
-Definition 10.1 -External ordering -
-
- -Fix a [total order](https://en.wikipedia.org/wiki/Total_order) $\preceq$ on the finite universe $U_{\mathcal{R}}$. For -example, order first by number of vertices, then by height, then recursively -by sorted child lists and vertex labels. - -
-::: - -::: {.annotation .annotation--static #def-canonical-rep} -
-Definition 10.2 -Canonical representative -
-
- -For a realizable behavior vector $b$, define - -$$ -\operatorname{Can}_{\mathcal{R}}(b) -$$ - -to be the $\preceq$-least tree in $U_{\mathcal{R}}$ with behavior vector $b$. - -
-::: - -::: {.annotation .annotation--static #thm-canonical} -
-Theorem 10.3 -Canonical representative theorem -
-
- -After choosing the external order $\preceq$, every -$\sim_{\mathcal{R}}$-equivalence class has a unique selected canonical -representative. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Canonical representative theorem" data-exhibit-type="proof" data-exhibit-caption="Each class meets the finite totally ordered universe in a nonempty set with a unique least element."} - -:::: exhibit-body -By [Theorem 9.9](#thm-normal-universe), every class has at least one -representative in $U_{\mathcal{R}}$. Since $U_{\mathcal{R}}$ is finite and -totally ordered by $\preceq$, each nonempty subset has a unique least -element. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-no-uniqueness} -
-Remark 10.4 -No intrinsic uniqueness claimed -
-
- -The theorem does not claim that each class has a unique minimal tree in any -intrinsic sense. Different non-isomorphic trees of the same size may realize -the same behavior vector. The uniqueness is selected uniqueness after a -chosen tie-breaking order. - -
-::: - -## What has been proved and what has not - -- *Proved:* fixed-resource equivalence equals behavior-vector equality. -- *Proved:* exact sibling pumping is governed by the index and period of each - product contribution element $\gamma_b$. -- *Proved:* Boolean, cyclic, threshold, and hybrid threshold-residue monoids - have explicit pumping bounds. -- *Proved:* every fixed-resource class has a finite normal representative, - and an externally selected canonical representative. -- *Not proved:* any global decomposition theorem for arbitrary finite - commutative monoids. -- *Not claimed:* intrinsic uniqueness of minimal representatives. -- *Not proved:* comparison with order-$r$ profiles. -- *Not proved:* nondefinability or definability of pursuit-evasion - properties. - -## Conclusion - -The fixed-resource monoid-aggregated model now has a sharper structural core. -The essential invariant for sibling multiplicities is the index-period pair -of the product contribution element $\gamma_b$. This converts the original -crude finite-product pumping lemma into an exact normal-form statement. It -also clarifies the qualitative meanings of the standard monoid families: -Boolean semilattices track support, cyclic groups track residue, threshold -monoids track saturation, and hybrids combine these effects. - -The global canonical-form theory is also cleaner than expected. Sibling -pumping bounds branching; size-minimality bounds height, because a repeated -behavior vector along a path could be contracted. Therefore every -fixed-resource equivalence class has a representative in a finite universe, -and canonical representatives exist after external tie-breaking. - -The next mathematical frontier is no longer fixed-resource equivalence -itself. That relation is fully finite and behavior-vector controlled. The -hard questions concern how separation cost grows as one varies the allowed -multiplicity observations, state sets, and monoids, and whether -pursuit-evasion properties cut across the resulting bounded-resource -theories. - -::::: aftermatter - -## Appendix A — Algorithmic consequences - -The theory is constructive, although often computationally enormous. - -::: {.annotation .annotation--static #prop-decidability} -
-Proposition A.1 -Decidability for fixed resources -
-
- -For fixed finite resource data $\mathcal{R}$ and finite rooted cop-labeled -trees $X, Y$, it is decidable whether - -$$ -X \sim_{\mathcal{R}} Y. -$$ - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Decidability for fixed resources" data-exhibit-type="proof" data-exhibit-caption="Enumerate the finite class D(R), evaluate both trees bottom-up, compare all coordinates."} - -:::: exhibit-body -The class $D(\mathcal{R})$ is finite by [Lemma 2.7](#lem-cardinality). One -may enumerate all summaries $P \in D(\mathcal{R})$, compute $P(X)$ and $P(Y)$ -bottom-up, and compare all coordinates. By [Theorem -3.3](#thm-behavior-vector), the trees are equivalent iff all coordinates -agree. [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #prop-computable-canonical} -
-Proposition A.2 -Computable canonical representative, in principle -
-
- -For fixed $\mathcal{R}$, a chosen external order $\preceq$ on -$U_{\mathcal{R}}$, and an input tree $T$, the canonical representative of the -class of $T$ is computable by finite search. - -
-::: - -::: {.exhibit .exhibit--proof data-exhibit-name="Computable canonical representative, in principle" data-exhibit-type="proof" data-exhibit-caption="Compute β_R(T), then scan U_R in ≼-order for the first tree with the same behavior vector."} - -:::: exhibit-body -Compute $b = \beta_{\mathcal{R}}(T)$ by enumerating $D(\mathcal{R})$. Then -enumerate the finite universe $U_{\mathcal{R}}$ in $\preceq$-order and return -the first tree $U$ with $\beta_{\mathcal{R}}(U) = b$. Termination follows from -[Theorem 9.9](#thm-normal-universe). [□]{.proof-qed} -:::: - -::: - -::: {.annotation .annotation--static #rem-practical} -
-Remark A.3 -Practical versus theoretical computation -
-
- -The bounds involving $|D(\mathcal{R})|$ are generally huge. The point of the -theorem is structural finiteness and conceptual normalization, not immediate -efficient implementation. For special monoid families, the exact -index-period bounds above are the first route toward usable computations. - -
-::: - -## Appendix B — Resource-growth separation complexity - -For fixed $\mathcal{R}$, equivalence is completely characterized by the -behavior vector. The more interesting long-term invariant appears when -resources vary. - -::: {.annotation .annotation--static #def-resource-family} -
-Definition B.1 -Resource family -
-
- -A *resource family* $\mathcal{F}$ is a collection of finite resource data -$\mathcal{R}$. Examples include: - -1. support-only resources with bounded $|S|$; -2. threshold resources with threshold $T \leq t$ and $|S| \leq s$; -3. cyclic resources with modulus $q \leq Q$ and $|S| \leq s$; -4. hybrid threshold-residue resources with bounded thresholds, moduli, and - state counts. - -
-::: - -::: {.annotation .annotation--static #def-separation} -
-Definition B.2 -Separation over a resource family -
-
- -Given a resource family $\mathcal{F}$, say that $X$ and $Y$ are *separated by -$\mathcal{F}$* if there exists $\mathcal{R} \in \mathcal{F}$ and $P \in -D(\mathcal{R})$ such that - -$$ -P(X) \neq P(Y). -$$ - -Equivalently, $\beta_{\mathcal{R}}(X) \neq \beta_{\mathcal{R}}(Y)$ for some -$\mathcal{R} \in \mathcal{F}$. - -
-::: - -::: {.annotation .annotation--static #def-separation-cost} -
-Definition B.3 -Separation cost, schematic -
-
- -Let $\kappa(\mathcal{R})$ be a chosen cost of a resource datum, for example a -tuple involving $|A|$, $|S|$, $|M|$, the threshold parameter, the modulus, or -the description length of $\mu$ and $\oplus$. Define - -$$ -\operatorname{sep}_{\mathcal{F}}(X, Y) -$$ - -to be the least cost of a resource datum $\mathcal{R} \in \mathcal{F}$ -separating $X$ and $Y$, and set $\operatorname{sep}_{\mathcal{F}}(X, Y) = -\infty$ if no $\mathcal{R} \in \mathcal{F}$ separates them. - -
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-Remark B.4 -Why games are deferred -
-
- -For fixed $\mathcal{R}$, a -[game characterization](https://en.wikipedia.org/wiki/Ehrenfeucht%E2%80%93Fra%C3%AFss%C3%A9_game) -is nearly tautological: -Spoiler can choose a differing coordinate $P \in D(\mathcal{R})$ if one -exists, and otherwise Duplicator wins because behavior vectors agree. A -nontrivial game should therefore characterize resource growth, restricted -resource families, or bounded access to coordinates, not merely the -fixed-$\mathcal{R}$ relation. In particular, the interesting game will need to -encode a budget on which coordinates $P$ Spoiler is permitted to access at -each round, with cost tied to $\kappa$. - -
-::: - -## Appendix C — Near-term theorem targets - -The present note proves the first three targets below and sets up the rest. - -- **T1. Exact sibling pumping.** Child counts of behavior type $b$ reduce by - the index-period pair of $\gamma_b$. Proved in [Theorem - 6.2](#thm-sibling-pumping). -- **T2. Canonical family bounds.** Boolean, cyclic, threshold, and hybrid - monoids have explicit pumping signatures. Proved in [Section - 7](#canonical-monoid-families). -- **T3. Finite normal representatives.** Every fixed-resource class has a - representative in a finite normal universe. Proved in [Theorem - 9.9](#thm-normal-universe). -- **T4. Efficient special-case canonicalization.** For concrete resource - families, replace the huge all-summary behavior vector by smaller - sufficient invariants. -- **T5. Separation complexity examples.** Compute exact or asymptotic costs - for one-node, star, unary-chain, and split/concentrated families under - support, threshold, cyclic, and hybrid resources. -- **T6. Resource-growth games.** Design a game that characterizes bounded - resource families rather than fixed-$\mathcal{R}$ equality of behavior - vectors. -- **T7. Pursuit-evasion tests.** Only after the previous items, ask whether - local pursuit properties are definable or separable in specific resource - families. - -::::: diff --git a/content/essays/index-period-normal-forms/mark.svg b/content/essays/index-period-normal-forms/mark.svg deleted file mode 100644 index ddbf638..0000000 --- a/content/essays/index-period-normal-forms/mark.svg +++ /dev/null @@ -1,70 +0,0 @@ - - A small rooted tree above an index-period rho-orbit, joined by a dashed abstraction arrow - A frontispiece mark for "Index-Period Normal Forms for Monoid-Aggregated Recursive Summaries." The upper figure is a small rooted tree with one node marked: the child whose contribution is being analyzed. The lower figure is a rho-shape orbit — a pre-periodic tail of three points leading into a four-cycle — the classical picture of an element's index and period in a finite monoid. The dashed arrow between them is the paper's central move: abstract from the combinatorial tree to the algebraic invariant of one element's contribution. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -