ShrinkChain: Forster's four-level shrinking chain (finiteness-and-chi) #
Unit: finiteness-and-chi (docs/design/finiteness-and-chi.md D3, Β§4.2, proof plan Β§6.4).
ShrinkChain X packages Forster's π β π β π β π* same-index-set shrinking chain (D3): U*
chart disks (Leray-good), U the level whose closure sits inside U*, V the Montel-compact
middle level, W the coboundary level whose closure sits inside V. All four induced
FinCover β€s share the same index set, so every refinement map between them is Ο = id
(ref_star_U/ref_star_V/ref_star_W/ref_U_V/ref_V_W/ref_U_W) β no Ο-plumbing ever
enters the norm layer.
Existence (ShrinkChain.nonempty) iterates the cech exists_chartDisk_closure_basis pattern
four times per point (chart disk β level 1 β level 2 β level 3), then extracts a finite subcover
of the innermost level W, reindexed by Finset.equivFin exactly as Cech.Covers's
exists_good_refinement_closure does.
Also provides the Banach cochain layer at one level P β {U, V, W}: NC0/NC1 (finite Pis
of BddHoloOn), deltaCLM (the 0-to-1 coboundary, Cech's d0 transposed to the norm
layer), NZ1 (bounded cocycles, packaged as ContinuousLinearMap.ker of an internal d1NC β
closed and complete "for free", no hand-rolled pointwise-condition closedness proof needed),
resNC0/resNC1 (restriction CLMs between same-index levels), the cocycle-relation workhorse
NZ1.rel_res (mirrors Cech.Refinement's Z1.rel_res), resNC1_mapsTo_NZ1 (mirrors
resC1_mem_Z1), and resZ (restriction of bounded cocycles, via
ContinuousLinearMap.codRestrict).
Finally, Forster's 14.6(b) Banach geometry (Β§4.2, Β§5 step 1): tradeDefect (the defect CLM
(ΞΆ, ΞΎ, Ξ·) β¦ ΞΆ|π β ΞΎ|π β Ξ΄π Ξ· on ZΒΉ(π) Γ ZΒΉ(π) Γ Cβ°(π)), tradeSpace (Forster's subspace
L β ZΒΉ(π) Γ ZΒΉ(π) Γ Cβ°(π), its ContinuousLinearMap.ker β complete for free), the
membership unfolders mem_tradeSpace_iff/mem_tradeSpace_iff_eq, and the two Schwartz-cospan
projections tradePi (Ο = prβ, the leg TradeBounded.lean proves surjective) and
tradeCompact (v = res_UV β prβ, the Montel-compact leg), plus registered instance
shortcuts on β₯(NZ1 T P)/β₯(tradeSpace T) that make the surrounding instance searches
reliable (see the note above NZ1's instances and the resolution note at the end of this
file β the former TODO(blocker) is RESOLVED). Still deferred (NOT instance-blocked, just
not built here): the two IsCompactOperator assembly lemmas of design Β§4.4
(isCompactOperator_resZ_UV, isCompactOperator_tradeCompact) β see the end-of-file note.
Nothing here uses the forbidden tactic.
Forster's π β π β π β π* with π* chart disks; same index set (D3).
- n : β
The number of chart centres in the chain.
The chart centres.
- Ustar : Fin self.n β TopologicalSpace.Opens X
The outermost opens, each inside its centre's chart source.
- U : Fin self.n β TopologicalSpace.Opens X
- V : Fin self.n β TopologicalSpace.Opens X
- W : Fin self.n β TopologicalSpace.Opens X
The innermost opens, which still cover
X. - isChartDisk_Ustar (i : Fin self.n) : Cech.IsChartDisk (self.Ustar i)
Instances For
Opens-level β€ forms of the chain inclusions β the shapes restrictCLM/resNC1/resZ
consume (definitionally the same statements as the Set-level _subset_ lemmas above).
The four FinCover β€s induced by a ShrinkChain. Reducible: their fields must unfold at
implicit transparency, or applications like C1 D T.coverW are not type-correct there and
every rewrite in such a goal fails.
Instances For
The cover of X by the V-level opens.
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The cover of X by the U-level opens.
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The cover of X by the outermost Ustar-level opens.
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Existence of a ShrinkChain (Β§6.4): iterate the cech chart-disk-with-compact-closure
basis four times per point, then extract a finite subcover of the innermost level.
Banach cochain layer at a level P β {U, V, W} #
0-cochains at level P (a finite Pi of BddHoloOns).
Equations
- RS.Finiteness.NC0 T P = ((i : Fin T.n) β β₯(RS.Finiteness.BddHoloOn (P i)))
Instances For
1-cochains at level P (full product over ordered pairs, no i < j convention β matches
cech's D5 convention).
Equations
- RS.Finiteness.NC1 T P = ((p : Fin T.n Γ Fin T.n) β β₯(RS.Finiteness.BddHoloOn (P p.1 β P p.2)))
Instances For
(Ξ΄β°f)_{ij} = f_j β f_i (after restriction to P i β P j); the Banach-layer analogue of
Cech.d0.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The 1-to-2-cochain coboundary at level P, purely internal (used only to package NZ1
as a continuous-kernel submodule β no NC2 is ever exported).
Equations
- One or more equations did not get rendered due to their size.
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Bounded cocycles: the kernel of d1NC, a closed submodule (ContinuousLinearMap.ker)
β Banach for free (ContinuousLinearMap.completeSpace_ker), no hand-rolled pointwise-condition
closedness proof needed.
The norm-bounded cocycles at level P: the kernel of the bounded coboundary d1NC.
Equations
- RS.Finiteness.NZ1 T P = (β(RS.Finiteness.d1NC T P)).ker
Instances For
The cocycle-relation workhorse (mirrors Cech.Refinement's Z1.rel_res): any
cocycle-relation triple, restricted to any smaller open W (via arbitrary β by proof
irrelevance, any β witnessing inequalities).
Restriction of 0-cochains along a same-index shrinking P' β€ P.
Equations
- RS.Finiteness.resNC0 T P P' h = ContinuousLinearMap.pi fun (i : Fin T.n) => RS.Finiteness.restrictCLM β― βSL ContinuousLinearMap.proj i
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Restriction of 1-cochains along a same-index shrinking P' β€ P.
Equations
- RS.Finiteness.resNC1 T P P' h = ContinuousLinearMap.pi fun (p : Fin T.n Γ Fin T.n) => RS.Finiteness.restrictCLM β― βSL ContinuousLinearMap.proj p
Instances For
Restriction takes bounded cocycles to bounded cocycles (naturality of d1NC, via the
NZ1.rel_res workhorse β mirrors Cech.Refinement's resC1_mem_Z1).
Restriction of bounded cocycles between same-index levels.
Equations
- RS.Finiteness.resZ T P P' h = (RS.Finiteness.resNC1 T P P' h βSL (RS.Finiteness.NZ1 T P).subtypeL).codRestrict (RS.Finiteness.NZ1 T P') β―
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Forster 14.6(b): the trade subspace L and its two Schwartz-cospan projections #
Forster 14.6(b)'s defect map (ΞΆ, ΞΎ, Ξ·) β¦ ΞΆ|π β ΞΎ|π β Ξ΄π Ξ· on the triple product
ZΒΉ(π) Γ ZΒΉ(π) Γ Cβ°(π) (Β§4.2/Β§5 step 1); its kernel is Forster's subspace L
(tradeSpace).
Equations
- One or more equations did not get rendered due to their size.
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Forster's subspace L (14.6(b)): triples (ΞΆ, ΞΎ, Ξ·) with ΞΆ = ΞΎ + δη on π,
packaged as ContinuousLinearMap.ker (closed, hence complete for free).
Equations
- RS.Finiteness.tradeSpace T = (β(RS.Finiteness.tradeDefect T)).ker
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Membership in L, rearranged to Forster's ΞΆ = ΞΎ + δη shape on each π-pair (the form
TradeBounded.lean's Β§5 steps 2/6/8 consume).
The surjective leg Ο : L βL ZΒΉ(π), (ΞΆ, ΞΎ, Ξ·) β¦ ΞΎ (14.6(b)'s projection;
surjectivity = the qualitative trade, proved in TradeBounded.lean as tradePi_surjective;
the norm constant of 14.6(b) is recovered inside schwartz_finite_cospan by
exists_preimage_norm_le β design Β§5 step 7).
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- One or more equations did not get rendered due to their size.
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The compact leg v : L βL ZΒΉ(π), (ΞΆ, ΞΎ, Ξ·) β¦ ΞΆ|π (compactness = Montel, assembled
from isCompactOperator_restrictCLM β deferred, see the end-of-file note).
Equations
- One or more equations did not get rendered due to their size.