Generic counting and Fox-calculus helpers #
Words evaluated at an H-translated marking differ by an H-element
(GExpr.eval_map through the H-quotient; no induction needed).
Shadow invariance under conjugation-trivial translations: if every
H-element acts trivially on the kernel module, translating the marking by an
H-tuple leaves every Fox shadow unchanged (the foxShadow_perturb_eq
induction, at a translating subgroup instead of the kernel itself).
The T̃-kernel of the cover and the operator trivialities #
T̃ ≤ B_λ as an elementary kernel (lem:radicaledge step 1 packaged):
normal, wild, θ-dead, abelian of exponent 2 — the carrier of the twist
calculus at the cover.
Equations
- Q2Presentation.Induction.tCoverKernel chief K lam hinv hne = { N := Q2Presentation.Induction.tCover chief K lam hinv, normal := ⋯, le_LY := ⋯, theta_dies := ⋯, comm := ⋯, exp2 := ⋯ }
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The deck kernel is central, so every conjugation operator on it is trivial.
M̃-conjugation is trivial on the T̃-kernel (mCover_conj_fix, operator
form) — the fibre-uniformity input.
The ω₂-residue at the cover order is odd (the deck kernel has order 2,
so 2 ∣ |B_λ|).
The deck-kernel Fox collapse #
Central-kernel Fox collapse: all operators on the deck kernel are
trivial, so any shadow is the exponent-sum diagonal (the relative
fixed-shadow lemma at W := ⊤, floor ⊥).
The deck-kernel shadow of either relator is the τ-slot.
Deck-kernel perturbations shift a relator value by exactly the τ-slot.
The two-element deck kernel is read injectively by relRead.
Cover markings and the obstruction bit #
Framing readout of a quotient framed target on a projected element.
A cover marking over a weak M-lift: generator values in B_λ
projecting to the lift's marking, framed by the parent frame.
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Cover framing is the child framing of the projection.
Every weak M-lift carries a cover marking (choice of
p_λ-preimages; framing descends).
Equations
- Q2Presentation.Induction.coverMarkingOf chief K lam hinv f a = Classical.choose ⋯
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Wild generator values of a cover marking land in the cover's L_Y
(the frame pins the tame coordinate).
Relator values of a cover marking lie in the deck kernel.
The cover projection as a hom of finite discrete profinite groups
(the stratumInclHom idiom).
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The obstruction bit of a cover marking: the relRead-sum of the two
relator defects (eq:edgevariationobstruction's ob, in-tree form).
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obRead is well-defined on the lift: any two cover markings over the
same weak M-lift differ by a deck-kernel perturbation, which shifts both
defects by the same τ-slot — the sum is invariant.
The marking-level liftability criterion (lem:radicaledge's
ob(f) = 0 ⟺ liftable, in-tree): a weak M-lift is λ-liftable iff the
obstruction bit of any cover marking over it vanishes.
The variation formula and the edge pairing #
The edge pairing ⟨[u], ρ*[ε̄]⟩ of a T̃-tuple against the two
relators at a cover marking: the relRead-sum of the two T̃-shadows
(eq:edgevariationobstruction's correction term, ledger form).
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The exact variation formula (eq:edgevariationobstruction,
lem:radicaledge steps 5–6): perturbing a cover marking by a T̃-tuple
shifts the obstruction bit by exactly the edge pairing. Both markings must
lie over weak M-lifts (so all four defects live in the deck kernel).
Fibre-uniformity of the pairing #
Cover elements projecting into M' lie in M̃.
The pairing is fibre-uniform (lem:radicaledge step 4, ledger form):
markings over lifts with the same child image differ by an M̃-tuple, and
M̃-conjugation fixes T̃, so the two T̃-shadows — hence the pairing —
agree. This is the C-factorization of the edge class.
The twist involution on the fibre #
The generator marking of a weak M-lift.
Equations
- Q2Presentation.Induction.fMarking chief K f a = (ProfiniteGrp.Hom.hom ↑f) (Q2Presentation.gammaGen a)
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A T̃-element pushed down to the child M-kernel (T̃ ↠ T' ≤ M').
Equations
- Q2Presentation.Induction.tCoverPush chief K lam hinv t = ⟨(Q2Presentation.Lifting.scalarCoverProj (Q2Presentation.Induction.xrKernel chief K) lam hinv) ↑t, ⋯⟩
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The pushed tuple of a T̃-tuple.
Equations
- Q2Presentation.Induction.tPushTuple chief K lam hinv t a = Q2Presentation.Induction.tCoverPush chief K lam hinv (t a)
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A relator cocycle: a T̃-tuple whose pushed M'-shadow kills both
relators at the lift's marking — exactly the twists preserving hom-ness
(the marking form of Z¹_{Γ,ρ}(T)).
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The twisted marking kills a relator the lift kills, when the shadow vanishes.
The twisted marking is admissible.
The twist of a weak M-lift by a relator cocycle — again a weak
M-lift (the f ↦ f_u of lem:radicaledge step 5, marking form).
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The twist does not move the child image.
The twist preserves the fibration base.
The twist is an involution (T'-values square to 1).
Perturbing a cover marking by a T̃-tuple yields a cover marking of the
twisted lift.
The cocycle condition is fibre-uniform (rowMap_perturb_eq): lifts
with the same child image share their relator cocycles.
The conditional halving exit #
The isolated nonvanishing residue (lem:radicaledge step 6's
[ε̄] ≠ 0 ⟹ perfect-degree-one-duality clause): over every child
surjection, SOME weak M-lift carries a relator cocycle of nonzero edge
pairing. This — not the halving itself — is the remaining content of
sec7_edgeHalving_gammaA; dissolution program in
audit/BLOCKR_P8_DESIGN.md §10-P8D.
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The per-g halving from a flipping twist (lem:radicaledge step 6 +
prop:nonzeroedge's per-fibre clause): a relator cocycle with nonzero
pairing twists the fibre involutively and flips the obstruction bit, so
exactly half of each fibre is λ-liftable. This dissolves the halving
content of sec7_edgeHalving_gammaA down to EdgeTwistFlip.