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LeanPool.BrillNoetherGraphs.LowGenus.GenusFiveBridgeRows

Articulation data for the four genus-five cubic bridge rows #

All four exceptional rows in the public cubic atlas have the same labelled genus-two lobe on vertices {0,1,2}, attached to the complementary genus-three side at vertex 0. The occurrence-level core cut checker and the factor-genus calculator verify this finite structural data directly.

The root-double bridge cut, with gluing vertex zero and left vertex set {0, 1, 2}.

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    The one-chord bridge cut, with gluing vertex zero and left vertex set {0, 1, 2}.

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      The square bridge cut, with gluing vertex zero and left vertex set {0, 1, 2}.

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        The double-matching bridge cut, with gluing vertex zero and left vertex set {0, 1, 2}.

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          theorem AtanasovRanganathan.GenusFiveBridgeRows.bnExists_face_of_two_three_cut (genusFour : Utilities.GenusFourRankOneExistence) {n p : ℕ} (core : Utilities.Certificate.ExplicitPotential.Core n p) (hn : 0 < n) (hLoopless : ∀ (edge : Fin p), core.tail edge ≠ core.head edge) (hConnected : core.Connected) (cut : Utilities.Certificate.CoreVertexCut.Data core) (hValid : cut.Valid) (hLeft : cut.leftGenus = 2) (hRight : cut.rightGenus = 3) (length : Fin p → ℕ) (hForest : Utilities.Certificate.ContractionForestCensusGeneral.IsForest core (Configurations.zeroSlots length)) (hNotLoopy : ¬Utilities.Certificate.ContractionForestCensusGeneral.IsLoopy core (Configurations.zeroSlots length)) :
          Utilities.BNExists (Configurations.faceSpec core hn length hForest hNotLoopy).graph 1 4

          A checked (2,3) articulation on a genus-five core supplies a degree-four pencil on every nonloopy forest face of that core.

          The four bridge rows are all closed structurally by the same checked (2,3) articulation.