OAI/GroupTheory/PolycyclicRecognition/Analysis/CompactProbeSequence.lean

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Compact good-probe sequences with harmless initial values

  1. theorem OAI.PolycyclicRecognition.choose_compact_good_probe_sequence line 16

    Source documentation

    Extend the eventual Fubini selection to sequences defined at every scale. Initial exceptional scales use the full compact probability space; the actual good-probe property is retained eventually.

    theorem choose_compact_good_probe_sequence
        {X : Type*} [Nonempty X] {Y : ℕ → Type*}
        [∀ n, TopologicalSpace (Y n)] [∀ n, CompactSpace (Y n)]
        [∀ n, T2Space (Y n)] [∀ n, MeasurableSpace (Y n)] [∀ n, BorelSpace (Y n)]
        (ν : ∀ n, ProbabilityMeasure (Y n)) (Good : ∀ n, X → Set (Y n) → Prop)
        (h : ∀ᶠ n in atTop, ∃ x K, IsCompact K ∧ Good n x K ∧
          (1 / 4 : ℝ≥0∞) < (ν n : Measure (Y n)) K) :
        ∃ (x : ℕ → X) (K : ∀ n, Set (Y n)),
          (∀ n, IsCompact (K n) ∧ MeasurableSet (K n) ∧
            (1 / 4 : ℝ≥0∞) < (ν n : Measure (Y n)) (K n)) ∧
          ∀ᶠ n in atTop, Good n (x n) (K n) := by
    …