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Theorem 1.15 (Béguin–Bonatti–Yu): a transitive Anosov flow with infinitely many nonisotopic transverse tori

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AnosovPlugs.thm_1_15_infinitely_many_transverse_tori

by Lucas · Oct 1, 2026 · Mathlib 0df444a (Lean v4.33.1)

3-manifoldsanosov-flowsdynamical-systemshyperbolic-dynamics

There exists a transitive Anosov vector field ZZZ on a closed orientable three-manifold MMM such that there exist infinitely many pairwise nonisotopic tori embedded in MMM and transverse to ZZZ:

∃(Tn)n∈N: Tn⋔Z,m≠n⇒Tm̸∼isotopyTn.\exists (T_n)_{n\in\mathbb N}:\ T_n \pitchfork Z,\quad m\neq n\Rightarrow T_m \not\sim_{\text{isotopy}} T_n.∃(Tn​)n∈N​: Tn​⋔Z,m=n⇒Tm​∼isotopy​Tn​.

Formalization Note Tori are C¹ embeddings of S1×S1S^1\times S^1S1×S1; isotopy is C¹ isotopy through embedded tori, up to reparametrisation of the final torus.

Preamble
import Mathlib
import Definitions.Def_AnosovPlugs_Tori
import Definitions.Def_AnosovPlugs_Hyperbolic

open scoped Manifold ContDiff Topology
open Set
Formal statement
namespace AnosovPlugs

theorem thm_1_15_infinitely_many_transverse_tori :
    ∃ (M : Type) (_ : TopologicalSpace M) (_ : ChartedSpace (EuclideanHalfSpace 3) M)
      (_ : IsManifold I3 ∞ M) (_ : T2Space M) (_ : CompactSpace M) (_ : ConnectedSpace M)
      (_ : BoundarylessManifold I3 M), IsOrientable M ∧
      ∃ Z : (x : M) → TangentSpace I3 x, IsAnosov Z ∧ IsTransitiveFlow Z ∧
        ∃ f : ℕ → Circle × Circle → M, (∀ n, IsTransverseTorus Z (f n)) ∧
          ∀ m n, m ≠ n → ¬ ToriIsotopic (f m) (f n) := by sorry

end AnosovPlugs
Source
F. Béguin, C. Bonatti, B. Yu, *Building Anosov flows on 3-manifolds*, Geom. Topol. 21 (2017) 1837–1930, https://doi.org/10.2140/gt.2017.21.1837, p. 1847, Theorem 1.15 (proof in §11)
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What the Lean code literally says, in plain math · Aristotle (Harmonic) — same agent as the drafter; non-blind

Non-blind read-back — not independent testimony. This read-back was written by the same agent (Aristotle, by Harmonic) that drafted the Lean statements, with full knowledge of the source paper and of the intended meaning. It was NOT produced by an independent, blind auditor, and no reviewer should treat it as independent confirmation that the code says what the paper says. Compare it against the Lean code yourself.

Conclusion only: there exist a type MMM with a topology, a charted-space structure over the half-space {x0≥0}⊂R3\{x_0\ge0\}\subset\mathbb R^3{x0​≥0}⊂R3, a C∞C^\inftyC∞ manifold structure, Hausdorff, compact, connected, and boundaryless (every point is an interior point), which is orientable (IsOrientable), a vector field ZZZ on MMM with IsAnosov ZZZ and IsTransitiveFlow ZZZ, and a sequence fn:S1×S1→Mf_n:S^1\times S^1\to Mfn​:S1×S1→M (n∈Nn\in\mathbb Nn∈N) such that each fnf_nfn​ is a C1C^1C1 injective immersion with Z(fn(p))∉im⁡D(fn)pZ(f_n(p))\notin\operatorname{im}D(f_n)_pZ(fn​(p))∈/imD(fn​)p​ for all ppp, and for m≠nm\neq nm=n there is no C1C^1C1 map F:R×(S1×S1)→MF:\mathbb R\times(S^1\times S^1)\to MF:R×(S1×S1)→M with each F(t,⋅)F(t,\cdot)F(t,⋅) (t∈[0,1]t\in[0,1]t∈[0,1]) an embedded torus, F(0,⋅)=fmF(0,\cdot)=f_mF(0,⋅)=fm​ and image of F(1,⋅)F(1,\cdot)F(1,⋅) equal to the image of fnf_nfn​.

Human review
  • Endorsed by Shuze Chen · Oct 1, 2026

    Confirmed by the moderator at approval.

  • Endorsed by Lucas · Oct 1, 2026

    Confirmed by the mission captain (proposal self-audit).

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