The exceptional members under restriction to a smaller open #
Statement. Restricting a piece's run to a smaller relatively compact open W' ⊆ W deletes the
blow-ups whose centres miss W' (the functor's CommutesWithOpenEmbeddings: the run over W' is
the cleaned pull-back ((run over W).pullback incl).eraseEmpty; the compatibility of
[Kol07, 34.1] and [Wlo09, Theorem 2.0.2(5)]). The theorem
BlowUpSequence.exists_orderEmb_totalTransformSeqFrom_last_pullback_eraseEmpty says what this does
to the BOUNDARY FAMILY at the last stage: along the lift λ := h_r ∘ eraseEmptyLast⁻¹ of a local
isomorphism h there is an order embedding ε of the cleaned run's index type into the original
run's with λ⁻¹(H_{ε i}) = H'_i for every member i and λ⁻¹(H_b) = ∅ outside the range of ε —
the members whose creation steps were deleted have empty trace over W' (the empty blow-ups
arising from restriction, [Kol07, Warning 20]: these are ONE source of empty traces, not the only
one). PieceEmbedding.exists_orderEmb_totalTransformSeq_last_liftOfLe is its instance at a piece,
along the lift liftOfLe of the open inclusion W' ↪ W.
Why. The restriction to a smaller open is the first and last leg — (γ) in the notation of
LocalResolutionShear.lean — of the transition of localResolution_independent_local,
(γ)·(α)⁻¹·(β)·(α)·(γ)⁻¹, and the only leg where the correspondence of the boundary families is a
proper injection.
Conventions. The list-level theorem is stated for an arbitrary start family F
(totalTransformSeqFrom); the exceptional family is the instance F := HypersurfaceFamily.empty M
(totalTransformSeqFrom_empty, definitional) with (empty M).comap h = empty N
(HypersurfaceFamily.empty_comap). The lift is spelled as the lemmas it rests on spell it: the
composite of Diffeomorph.toAnalyticMap eraseEmptyLast.symm and pullbackLiftLast, coerced to
functions.
Sources. The lift of a local isomorphism to the blow-ups, [Kol07, Definition 30.1]; the empty
blow-up convention, [Kol07, 32] and [Kol07, 34.1]; [Wlo09, Theorem 2.0.2(5)]. The proofs compose
totalTransformSeqFrom_last_pullbackLiftLast (OrderReduction/ConcatPullback.lean) with
eraseEmptyIdx/hyp_eraseEmptyIdx/hyp_eq_empty_of_notMem_range_eraseEmptyIdx
(Functor/EraseEmptyBoundary.lean); not in the sources.
The boundary family of the CLEANED pull-back (h^* L).eraseEmpty at its last stage against
the boundary family of L ([Kol07, Definition 30.1]; the empty blow-up convention [Kol07, 32],
[Kol07, 34.1]), along the lift λ := h_r ∘ eraseEmptyLast⁻¹ of the local isomorphism h — an order
embedding ε of the cleaned list's index type into L's with λ⁻¹(H^L_{ε i}) = H^{cleaned}_i for
every i, and λ⁻¹(H^L_b) = ∅ for every b outside the range of ε. From
totalTransformSeqFrom_last_pullbackLiftLast and eraseEmptyIdx with hyp_eraseEmptyIdx,
hyp_eq_empty_of_notMem_range_eraseEmptyIdx.
The transport of a hypersurface family along an equality: an order isomorphism of the index types matching the members.
The boundary family at the last stage of an equal list, read through stageOfEq.
The manifold level at the piece: along the lift liftOfLe of the open inclusion W' ↪ W, the
last-stage boundary family over W' corresponds to the one over W — eraseEmptyIdx transported
along localResolutionSeq_of_le and empty_comap.