From merge sequences to locally definable construction sequences

Lax185574.MergeToConstruction · concepts/Lax185574/MergeToConstruction.lean · lax-185574

proven

Loading review…

Sign in with ORCID

Community review

Flags

Each flag is tied to a public ORCID identity and explains why this concept may be incorrect.

No flags have been submitted.

    Community review

    Flag this concept

    State precisely what appears incorrect. This explanation will be public under your ORCID name.

    No source line selected.

    Natural Language Statement

    Lemma

    For every n-vertex graph G and merge sequence (𝒫₁, R₁), …, (𝒫_ℓ, R_ℓ) of G, there is a construction sequence G₁, …, G_λ of G such that the following properties hold for all r ≥ 1. Let w_r be the radius-r width of the merge sequence.

    1. The obtained construction sequence has radius-r width at most w_r, and has length λ ≤ O(n w₁).
    2. Suppose for every i ∈ [ℓ], the relations ≡{𝒫_i} and R_i are definable in some expansion of G with 2 unary predicates, using two fixed first-order formulas of quantifier rank 5. Then, for every t ∈ [λ−1] and v ∈ V(G), the induced partial graph G_t[Ball^{G{t+1}}_r(v)] is definable in some expansion of G with 2ℓ+1 unary predicates, using formulas of quantifier rank 7 with w_r parameters.
    3. The construction sequence can be computed in time O(ℓ n²), given an n-vertex graph G and merge sequence of length ℓ.
    Concept map
    25 concepts
    100%
    Proven claimDefinitionThis conceptRelated conceptA → B: B builds on A
    Evidence

    Each proof establishes this claim relative to its assumptions.

    In the paper

    • page 37 of this submission's paper

    Lean source view on GitHub

    1import Lax185574.BetterMergeSequences
    2import Lax185574.ConstructionWidth
    3import Lax185574.LocalDefinability
    4import Lax185574.ConstructionSequences
    5
    6/-!
    7---
    8title: From merge sequences to locally definable construction sequences
    9type: lemma
    10---
    11For every n-vertex graph G and merge sequence (𝒫₁, R₁), …, (𝒫_ℓ, R_ℓ) of
    12G, there is a construction sequence G₁, …, G_λ of G such that the
    13following properties hold for all r ≥ 1. Let w_r be the radius-r width
    14of the merge sequence.
    15
    161. The obtained construction sequence has radius-r width at most w_r,
    17 and has length λ ≤ O(n w₁).
    182. Suppose for every i ∈ [ℓ], the relations ≡_{𝒫_i} and R_i are
    19 definable in some expansion of G with 2 unary predicates, using two
    20 fixed first-order formulas of quantifier rank 5. Then, for every
    21 t ∈ [λ−1] and v ∈ V(G), the induced partial graph
    22 G_t[Ball^{G_{t+1}}_r(v)] is definable in some expansion of G with
    23 2ℓ+1 unary predicates, using formulas of quantifier rank 7 with w_r
    24 parameters.
    253. The construction sequence can be computed in time O(ℓ n²), given an
    26 n-vertex graph G and merge sequence of length ℓ.
    27
    28# Formalization notes
    29
    30The construction sequence is produced by a function `script` of the
    31graph and the merge sequence, as a script of
    32`Lax185574.ConstructionSequences`, and the algorithm `A` computes this
    33function, in the sense of `Lax185574.Algorithms`. The algorithm, the
    34constant `c` of the time bound O((ℓ+1) · (n+1)²) and the constant `K` of
    35the length bound come first, so both constants are absolute. The input
    36is the pair (G, merge sequence). A graph has the vertices `Fin n`, and
    37the notions of merge sequences and construction sequences are applied
    38to its `SimpleGraph`.
    39
    40A merge sequence is one in the sense of `Lax185574.MergeSequences`, so
    41𝒫₁ is the partition into singletons and 𝒫_ℓ = {V(G)} by its definition.
    42
    43The width of item 1 is the radius-r width of
    44`Lax185574.ConstructionWidth`, which counts parts. The length bound
    45O(n w₁) is spelled out as K · (n+1) · (w₁+1). The radius-r width of the
    46merge sequence is `MergeSequences.mergeWidth`. The definability
    47hypothesis of item 2 is `BetterMergeSequences.StagesDefinable` for some
    48two formulas of quantifier rank at most 5, and the conclusion is
    49`LocalDefinability.IsRadiusDefinable` with 2ℓ+1 predicates, w_r
    50parameters and rank 7.
    51
    52**Deviation from the paper.** Both bounds use max(1, w_r) instead of
    53w_r. On a graph with one vertex the merge sequence of length 1 has width
    540, the maximum over an empty range, while every construction sequence
    55has width 1. For n ≥ 2 the two agree, since every merge sequence has
    56length at least 2 and width at least 1.
    57
    58Every number in the encoding of the script is at most the length of the
    59encoding plus n (`Script.HasSmallNumbers`). The paper does not say
    60this. An algorithm can ensure it by giving the vertices of the initial
    61partial graph the colors 0, …, n − 1. The bound lets the output be
    62passed on as in `Lax185574.DefinableSequences`.
    63-/
    64
    65namespace Lax185574.MergeToConstruction
    66
    67open FirstOrder FirstOrder.Language Lax710763.Transductions
    68open Lax185574.Graphs Lax185574.Algorithms
    69open Lax185574.Partitions Lax185574.MergeSequences Lax185574.BetterMergeSequences
    70open Lax185574.ConstructionSequences Lax185574.ConstructionWidth
    71open Lax185574.LocalDefinability Lax185574.FirstOrderTypes
    72
    73/-- **Merge sequences to construction sequences.** One algorithm
    74converts a merge sequence of length `ℓ` of a graph into a construction
    75sequence of the same graph, given by its script, in time
    76`O((ℓ+1) · (n+1)²)`. For every `r ≥ 1`, the construction sequence has
    77radius-`r` width at most `max 1 w_r`, where `w_r` is the radius-`r`
    78width of the merge sequence, and length at most `K · (n+1) · (w₁+1)`. If
    79two formulas of quantifier rank at most `5` define the stages, it is
    80radius-`r` definable with `2ℓ+1` predicates, `max 1 w_r` parameters and
    81rank `7`. -/
    82axiom exists_constructionSequence_of_mergeSequence :
    83 ∃ (A : Algorithm) (c K : ℕ) (script : (G : Graph) →
    84 List (Setoid (Fin G.n) × SimpleGraph (Fin G.n)) → Script G.n),
    85 ∀ (G : Graph) (ms : List (Setoid (Fin G.n) × SimpleGraph (Fin G.n))),
    86 IsMergeSequence G.toSimpleGraph ms →
    87 let σ := script G ms
    88 IsConstructionSequence G.toSimpleGraph σ.run ∧ σ.HasSmallNumbers ∧
    89 σ.run.length ≤ K * (G.n + 1) * (mergeWidth 1 ms + 1) ∧
    90 (∀ r : ℕ, 1 ≤ r →
    91 constructionWidth r σ.run ≤ max 1 (mergeWidth r ms) ∧
    92 ((∃ φeq φR : (withColors Language.graph 2).Formula (Fin 2),
    93 quantifierRank φeq ≤ 5 ∧ quantifierRank φR ≤ 5 ∧
    94 StagesDefinable G.toSimpleGraph ms φeq φR) →
    95 IsRadiusDefinable G.toSimpleGraph σ.run r (2 * ms.length + 1)
    96 (max 1 (mergeWidth r ms)) 7)) ∧
    97 A.Computes c (G, ms) σ ((ms.length + 1) * (G.n + 1) ^ 2)
    98
    99end Lax185574.MergeToConstruction
    100
    Show Proof
    Formalization notes

    The construction sequence is produced by a function scriptscript of the graph and the merge sequence, as a script of Lax185574.ConstructionSequencesLax185574.ConstructionSequences, and the algorithm AA computes this function, in the sense of Lax185574.AlgorithmsLax185574.Algorithms. The algorithm, the constant cc of the time bound O((ℓ+1) · (n+1)²) and the constant KK of the length bound come first, so both constants are absolute. The input is the pair (G, merge sequence). A graph has the vertices FinnFin n, and the notions of merge sequences and construction sequences are applied to its SimpleGraphSimpleGraph.

    A merge sequence is one in the sense of Lax185574.MergeSequencesLax185574.MergeSequences, so 𝒫₁ is the partition into singletons and 𝒫_ℓ = {V(G)} by its definition.

    The width of item 1 is the radius-r width of Lax185574.ConstructionWidthLax185574.ConstructionWidth, which counts parts. The length bound O(n w₁) is spelled out as K · (n+1) · (w₁+1). The radius-r width of the merge sequence is MergeSequences.mergeWidthMergeSequences.mergeWidth. The definability hypothesis of item 2 is BetterMergeSequences.StagesDefinableBetterMergeSequences.StagesDefinable for some two formulas of quantifier rank at most 5, and the conclusion is LocalDefinability.IsRadiusDefinableLocalDefinability.IsRadiusDefinable with 2ℓ+1 predicates, w_r parameters and rank 7.

    Deviation from the paper. Both bounds use max(1, w_r) instead of w_r. On a graph with one vertex the merge sequence of length 1 has width 0, the maximum over an empty range, while every construction sequence has width 1. For n ≥ 2 the two agree, since every merge sequence has length at least 2 and width at least 1.

    Every number in the encoding of the script is at most the length of the encoding plus n (Script.HasSmallNumbersScript.HasSmallNumbers). The paper does not say this. An algorithm can ensure it by giving the vertices of the initial partial graph the colors 0, …, n − 1. The bound lets the output be passed on as in Lax185574.DefinableSequencesLax185574.DefinableSequences.

    Discussion

    Ask a question or add context. Endorsements and structured flags are kept in the review panel above.

    Loading discussion…