Pairing-preserving connectivity #
The pairing-resolved value is well-defined once systems inducing the same boundary pairing are connected by pairing-preserving repair steps. This file fixes the step relation and the connectivity statement, proves that localized repairs qualify, and derives the same-pairing invariance of the signed summand from connectivity and the per-step ledger.
Two systems induce the same boundary pairing.
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- RS.EdgeSubset.SamePairing κ κ' = ∀ (δ : W.Flag) (hδ : δ ∈ F.boundaryFlags), κ.pathMatch δ hδ = κ'.pathMatch δ hδ
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Inducing the same boundary pairing is reflexive.
It is symmetric.
And transitive — an equivalence on transition systems.
A repair step that preserves the boundary pairing.
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A pairing-preserving step indeed preserves the pairing.
A composite move: a repair block whose net effect preserves the boundary pairing (individual repairs may cross two chains and change it; the double-crossing example shows single-step connectivity fails, and non-adjacent restorations force general blocks rather than pairs).
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A pairing-preserving move: a single preserved step or a π-restoring pair.
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- RS.EdgeSubset.MatchPreservingMove κ₁ κ₂ = (RS.EdgeSubset.MatchPreservingStep κ₁ κ₂ ∨ RS.EdgeSubset.PairedStep κ₁ κ₂)
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The connectivity statement (the keystone, move form): systems with the same boundary pairing are connected by pairing-preserving moves, up to match-equality at the endpoints. (Single steps do not suffice: the double-crossing configuration disconnects the fibre.)
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Connectivity is a theorem in the block form: any repair
chain between same-pairing systems is a single pairing-preserving
move, so the general connectivity of TransitionMove suffices.
The per-step ledger interface: every pairing-preserving step preserves the signed canonical summand (dischargeable from the localized/non-separated ledgers plus the orbit parities; two-path moves change the pairing and are excluded by the step relation).
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The MatchEq layer for the signed canonical summand.
The forward-carried chain induction: along a chain of pairing-preserving steps, a canonical orientation and the signed value propagate from the base.
The endpoint transfer: a canonical orientation and the signed
value cross a MatchEq to the target system.
Same-pairing invariance from connectivity and the step ledger: with these two inputs the signed canonical summand depends only on the boundary pairing — the well-definedness of the pairing-resolved value.