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A primitive pi torus collar has contracting longitude and exhausting plane caps
Statement
On the original Π torus, choose its primitive Π meridian β and a complementary longitude λ. Its one-sided longitude holonomy can be chosen strictly contracting. The collar longitude annuli grow the actual meridian caps, and their iterates exhaust each nearby leaf as a plane with limit set exactly the original torus. The limit set means ambient limits of sequences escaping every intrinsic compact subset of the leaf, equivalently the intersection of closures of tails of a cofinal compact exhaustion.
Facts & Assumptions
Given: The original Π torus leaf of the present foliation with its primitive meridian and a complementary longitude , and the one-sided longitude holonomy on a common small transversal.
The in-pair item A nonzero pi class on a torus has a primitive embedded pi root gives the primitive embedded meridian with identity one-sided holonomy and the embedded fence annulus with embedded disks bounded by each positive boundary; the in-pair item The canonical Jordan cap bundle develops coherently over every positive band supplies the coherent regular cap development from the reference fibre.
The in-pair item Compact leaves near a compact reference leaf are one-sheeted collar graphs supplies the finite-generator graph lemma: a compact nearby leaf through a sufficiently small base parameter of a compact leaf is a one-sheeted collar graph, preserving essential transported loops; the sibling-pair item lem-finite-chart-surface-normal-forms-supply-jordan-disks-and-torsion-free-groups supplies the surface-Jordan disk and the complement of a torus in the oriented surface, and The two-dimensional torus fixes the torus model.
The standing assumption is Countable Choice as recorded for this pair (The countable-choice principle used in the foliation pair).
Proof
The meridian has identity one-sided holonomy by [F1]. Suppose at a sufficiently small positive . Both generators then fix . Construct the nearby graph directly: cut along these generators, continue the plaque through along a finite tree of paths to a finite chart cover of the cut polygon, and shrink the base interval once so the finitely many transports and overlap homotopies are defined. Each overlap difference is a word in the two generators; holonomy invariance identifies its transverse transport with that word, which fixes . Thus the local plaque sections agree, including across the polygon edges. They give a compact graph over , contained in the leaf through . Its inclusion is locally open in that intrinsic leaf and its image is intrinsically compact, hence closed; connectedness makes the graph the whole leaf. Collar projection would make its transported meridian essential, contradicting the nullness supplied by [F1]. This existence argument is separate from [F2]'s assertion about leaves already known compact. Hence has no positive fixed point on one small connected interval. Replacing by its inverse if necessary gives ; its iterates decrease to zero, since any positive limit would be a fixed point.
Finite plaque transport over a cut fundamental polygon of the torus gives the actual collar suspension: identifies the meridian edges without transverse change and identifies the longitude edges by ; the construction uses finitely many compact chart relations, all valid after one common shrink. For each the longitude circuit thickened by the meridian coordinate gives an embedded leafwise annulus from to , whose base projection travels once over the complementary torus annulus. Two disjoint embedded null circles in a nonspherical oriented leaf joined by an annulus have nested Jordan disks whose difference is that annulus: otherwise the two disks and the annulus would form an open-and-closed sphere leaf.
The nesting direction is locally constant in by compact cap transport and the disjointness of the boundary circles. It cannot be shrinking: if the disk of lay inside the disk of , iteration would place every inside the compact disk of , but these circles approach the original torus, which is disjoint from that disk, contradicting the positive ambient distance between the two compact sets. Hence the disk relation is for every small .
The union of the increasing disks is the entire nearby leaf: given any point of that leaf, join it to a point of by a compact intrinsic path; its ambient image is compact and disjoint from the original compact torus, hence has positive distance from it, while the late boundary circles lie arbitrarily close to the torus and avoid that path, so the path cannot leave the late disk and its endpoint belongs to the union. An increasing union of disks with each compactly inside the next is a plane: choose successive disk and annulus homeomorphisms to concentric disks of radii and glue them, the exact differences providing the annuli. These annuli lie in collar heights tending uniformly to zero, so they have no limit points away from the original torus, while every point of the torus is approached because their meridian and longitude base projections cover the whole torus; the compact initial disk contributes no intrinsic end-limit points. Thus the leaf limit set is exactly the original torus. The limit-set convention is independent of the chosen exhaustion: any intrinsic compact subset is contained in a sufficiently late disk because the disks form an increasing open cover and compactness selects finitely many whose maximum contains it; intersecting closed exhaustion tails and the escaping-sequence definition agree in the compact metric ambient space by choosing one point from each shrinking rational neighbourhood and tail, using the standing countable choice of [F3].
Depends on
- The countable-choice principle used in the foliation pair
- A nonzero pi class on a torus has a primitive embedded pi root
- Compact leaves near a compact reference leaf are one-sheeted collar graphs
- The canonical Jordan cap bundle develops coherently over every positive band
- Finite surface normal forms, Jordan disks, and torsion control
- The two-dimensional torus $T^2=(\mathbb R/\mathbb Z)^2$
Used by
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Sources
- S. P. Novikov, The Topology of Foliations (complete English translation) (standard reference, not scraped)
- Mark Brittenham, Foliations and the Topology of 3-Manifolds, classes 11-20 (standard reference, not scraped)