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Reeblessness and tautness are not equivalent without extra hypotheses
Statement
Assume . For a smooth cooriented codimension-one foliation of a closed oriented three-manifold, tautness implies Reeblessness by A Reeb component obstructs tautness, but Reeblessness alone does not imply tautness.
Here is a closed example. On , with coordinates , put This is nowhere zero and , so its kernel defines a smooth cooriented foliation by The codimension-one Frobenius criterion. The tori and are leaves. On each intervening strip the other leaves satisfy with free, and are intrinsically cylinders. There are no plane leaves, so no saturated region can have the interior-plane foliation required by Reeb components of a codimension-one foliation. Thus the foliation is Reebless. The compact saturated region has the -positive normal pointing inward at both boundary tori. It is a dead-end component in Dead-end components, so the foliation is not taut by A foliation is taut if and only if it has no dead-end component.
Remarks
Ranz, Corollary 2.13(ii), printed pp.40–41, instead describes a noncompact strip product. Its strips are not compact dead-end components under this page's definition, so that terminology does not justify the closed-manifold comparison. The explicit torus construction above supplies the witness directly. The single-transversal conclusion additionally uses nonempty compact connected ambient manifolds, as stated in A taut foliation of a compact connected manifold has a single closed transversal.
Depends on
- A Reeb component obstructs tautness
- A foliation is taut if and only if it has no dead-end component
- A taut foliation of a compact connected manifold has a single closed transversal
- The countable-choice principle used in the foliation pair
- The codimension-one Frobenius criterion
- Dead-end components
- The two-dimensional torus $T^2=(\mathbb R/\mathbb Z)^2$
- Reeb components of a codimension-one foliation
Used by
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