Smooth concordance of smooth embeddings #
This file defines a globally collared smooth concordance between two smooth embeddings
f g : M → N. To avoid manifolds with boundary, a concordance is a C^n embedding
F : M × ℝ → N × ℝ which is a collared track from f to g (TauCeti.IsCollaredTrack): the
product f × id and g × id on uniform positive-width neighborhoods of the initial and final
ends, mapping M × (0, 1) into N × (0, 1).
Its restriction to M × [0, 1] is an ordinary smooth concordance which is a product near both
ends. The uniform collar widths are part of the data here, so this is stronger than merely requiring
an ordinary smooth concordance; no converse is asserted for noncompact M. The product ends make
globally collared concordances stack smoothly. For knots, M is the circle and the track is an
annulus in N × [0, 1]; this is the relation underlying the knot concordance group.
The relation is defined here for arbitrary smooth embeddings, in line with defining isotopy once
for general maps; smooth knot concordance is the case of TauCeti.SmoothCircleEmbedding, whose
source is the circle.
Main definitions #
TauCeti.SmoothEmbedding.Concordance f g: aC^nconcordance fromftog, in collared form.TauCeti.SmoothEmbedding.conjTime: a smooth embedding ofM × ℝintoN × ℝconjugated by an affine change of time, as a smooth embedding.TauCeti.SmoothEmbedding.Concordance.refl,symm,trans: the constant concordance, the reversed concordance, and the stacked concordance.TauCeti.SmoothEmbedding.Concordance.ofDiffeotopy: the trace of a diffeotopy, a concordance from an embedding to its image under the final diffeomorphism.TauCeti.SmoothEmbedding.Concordance.ofSmoothIsotopy: the collared trace of a compact-source smooth isotopy, as a concordance.TauCeti.SmoothEmbedding.Concordance.ofSourceDiffeotopy: the trace of a diffeotopy of the source, a concordance from an embedding to its reparametrization by the final diffeomorphism.TauCeti.SmoothEmbedding.Concordance.ofDiffeotopies: the trace of a diffeotopy of the target and one of the source run together, a concordance fromftoΦ.final ∘ f ∘ Ψ.final.TauCeti.SmoothEmbedding.Concordance.collaredSmoothTransitionUnit: the time reparametrization of these traces, a smooth transition from0to1constant near both ends.TauCeti.SmoothEmbedding.Concordant: the concordance relation.
Main results #
TauCeti.SmoothEmbedding.Concordant.equivalence: for a finite-dimensional ambient model, concordance is an equivalence relation.TauCeti.SmoothEmbedding.SmoothAmbientIsotopic.concordant: smoothly ambient isotopic embeddings are concordant.TauCeti.SmoothEmbedding.Concordant.of_smoothIsotopic: smoothly isotopic embeddings of a compact boundaryless source into a finite-dimensional Hausdorff boundaryless target are concordant.
Implementation notes #
Everything about a concordance that does not depend on the smoothness of its track — the time-level
lemmas, the reversed track TauCeti.reverseTime and the stacked track TauCeti.stack with its
embedding property — is inherited from TauCeti.IsCollaredTrack; this file only supplies the
smoothness of the reversed and stacked tracks. Stacking two concordances glues two immersions along
an open cover. Mathlib's Manifold.IsImmersion requires a single complement for all points, so the
glued map is shown to be an immersion with TauCeti.isImmersion_iff_forall_isImmersionAt, which
needs the model of N to be finite-dimensional. The same criterion for the isotopy track
requires that assumption in ofSmoothIsotopy as well as trans and statements depending on them.
The traces of diffeotopies and smooth isotopies are reparametrized by Real.smoothTransition,
which is C^∞ but not analytic; ofDiffeotopy, ofSourceDiffeotopy, ofDiffeotopies and
ofSmoothIsotopy therefore assume n ≤ ∞.
References #
- J. F. P. Hudson, Concordance, isotopy, and diffeotopy, Ann. of Math. 91 (1970), 425–448, for concordance of embeddings.
- C. Livingston, A survey of classical knot concordance, in Handbook of Knot Theory (2005), Section 2, for knot concordance.
A C^n concordance from the smooth embedding f to the smooth embedding g, in collared
form: a C^n embedding of M × ℝ into N × ℝ which is f × id and g × id on neighborhoods
of the initial and final ends, and maps M × (0, 1) into N × (0, 1).
- toSmoothEmbedding : SmoothEmbedding (I.prod (modelWithCornersSelf ℝ ℝ)) (J.prod (modelWithCornersSelf ℝ ℝ)) n (M × ℝ) (N × ℝ)
The track of the concordance, a smooth embedding of
M × ℝintoN × ℝ. - isCollaredTrack_toSmoothEmbedding : IsCollaredTrack ⇑f ⇑g ⇑self.toSmoothEmbedding
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Two smooth embeddings are concordant when there is a concordance from one to the other.
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Two smooth embeddings are concordant exactly when their concordance type is nonempty.
Affine changes of time #
The conjugate TauCeti.conjTime T a b of a smooth embedding T of M × ℝ into N × ℝ by the
affine change of time t ↦ a * t + b, a ≠ 0, as a smooth embedding.
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The underlying map of the conjugate smooth embedding is the conjugate map.
The underlying map of a concordance is that of its track.
Two concordances with the same track are equal.
The track of a concordance is a collared track from f to g.
At time 0 a concordance is its initial embedding.
At time 1 a concordance is its final embedding.
Diffeomorphisms #
An ambient diffeomorphism carries a concordance from f to g to one between the
transported embeddings.
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A diffeomorphism of the source reparametrizes a concordance from f to g into one between
the reparametrized embeddings.
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The constant and the reversed concordance #
The constant concordance from f to itself, whose track is f × id.
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The reversed concordance from g to f, obtained by reflecting time in 1 / 2.
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The track of the reversed concordance is the reversed track.
Reversing a concordance twice gives it back.
Stacking concordances #
The stacked concordance from f to h: the concordance F from f to g at triple speed
during [0, 1/3], then the constant concordance at g, then the concordance G from g to h
at triple speed during [2/3, 1].
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The track of the stacked concordance is the stacked track.
Before time 1 / 2 the stacked concordance runs the first concordance at triple speed.
After time 1 / 2 the stacked concordance runs the second concordance at triple speed.
Diffeotopies #
The time reparametrization t ↦ Real.smoothTransition (2 * t - 1 / 2) of the traces of
diffeotopies, as a map into the unit interval: a smooth transition from 0 to 1 which is
constant on neighborhoods of both ends of the unit interval.
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The collared smooth transition at t is Real.smoothTransition (2 * t - 1 / 2).
The collared smooth transition is C^n for every n ≤ ∞.
The collared smooth transition is continuous.
The collared smooth transition is 0 up to time 1 / 4.
The collared smooth transition is 1 from time 3 / 4 on.
The trace of a diffeotopy Φ of N: the concordance (x, t) ↦ (Φ (ρ t, f x), t) from f
to its image under the final diffeomorphism of Φ, where
ρ(t) = Real.smoothTransition (2 * t - 1 / 2).
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The collared trace of a smooth isotopy of a compact boundaryless source is a concordance. The time coordinate is retained, so intersections between different time slices cause no problem. The target is finite-dimensional, Hausdorff and boundaryless.
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The trace evaluates the isotopy at a smooth time transition constant near both ends.
The trace of a source diffeotopy Ψ of M: the concordance (x, t) ↦ (f (Ψ (ρ t, x)), t)
from f to its reparametrization by the final diffeomorphism of Ψ, where
ρ(t) = Real.smoothTransition (2 * t - 1 / 2).
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The trace of a source diffeotopy at (x, t) is f applied to the motion of x at the
reparametrized time Real.smoothTransition (2 * t - 1 / 2).
The trace of an ambient and a source diffeotopy run together: for diffeotopies Φ of N
and Ψ of M, the concordance (x, t) ↦ (Φ (ρ t, f (Ψ (ρ t, x))), t) from f to
Φ.final ∘ f ∘ Ψ.final, where ρ(t) = Real.smoothTransition (2 * t - 1 / 2). Unlike the stacked
traces of Φ and of Ψ, every time slice is Φₛ ∘ f ∘ Ψₛ for a single time s, so a property
of f preserved by all such conjugations holds along the whole concordance.
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The joint trace of an ambient and a source diffeotopy at (x, t) applies Ψ, then f, then
Φ, all at the reparametrized time collaredSmoothTransitionUnit t.
The concordance relation #
A concordance witnesses concordance.
Smoothly isotopic embeddings of a compact boundaryless source into a finite-dimensional Hausdorff boundaryless target are concordant.
An ambient diffeomorphism preserves concordance.
Reparametrizing the source by a diffeomorphism preserves concordance.
Concordance is reflexive.
Concordance is symmetric.
Concordance is transitive, for a finite-dimensional ambient model.
For a finite-dimensional ambient model, concordance is an equivalence relation on smooth embeddings.
Concordance of smooth embeddings, packaged as a setoid.
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The relation of the concordance setoid is concordance.
Smoothly ambient isotopic embeddings are concordant, through the trace of the diffeotopy.