Polygonal realization of Gallier--Xu P2 #
This file packages the local two-disk cut model from DiskSquare for finite cyclic
presentations. The first layer normalizes the cyclic position of a nondegenerate positively
oriented cut and supplies an exact selected-face homeomorphism. It is deliberately stated in
terms of the existing P2Cut data, so the presentation-level quotient comparison can use the
same side indices and no second formulation of P2 is introduced.
The selected source face has as many stored sides as the two linear cut pieces together.
Rotation of the linear cut word that recovers the stored source boundary. This version is used after reducing to the positive traversal orientation.
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The linear cut-word index carrying a stored source side.
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Cyclic alignment of the source boundary is injective on side indices.
Lookup at the rotated linear cut index recovers the stored source dart.
The selected source face, with its cyclic starting point aligned to the cut, is exactly the local one-polygon-to-two-child quotient model.
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Exact side computation for the cyclically aligned selected-face homeomorphism.
A rotated source side lying in the left cut piece, viewed with its local left index.
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A rotated source side lying in the right cut piece, viewed with its local right index.
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In the left branch, the local cut-piece lookup is the stored source dart.
In the right branch, the local cut-piece lookup is the stored source dart.
Exact selected-face computation for a side belonging to the left cut piece.
Exact selected-face computation for a side belonging to the right cut piece.
The fresh seam inside the actual split presentation #
Stored target index of the positive fresh dart in the selected child.
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Stored target index of the negative fresh dart in the right child.
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- LeanEval.Topology.ClassificationOfSurfaces.FiniteCyclicPresentation.P2.positiveRightFreshIndex P cut horientation = ⟨0, ⋯⟩
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The selected child's fresh-edge boundary occurrence.
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The right child's fresh-edge boundary occurrence.
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The exact reversed-parameter pairing carried by the fresh P2 seam.
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Embedding the local child quotient in the target realization #
Phantom side-count transport from the local selected child to the actual target face.
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Phantom side-count transport from the local right child to the actual target face.
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The target selected-child index corresponding to a local child side.
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- LeanEval.Topology.ClassificationOfSurfaces.FiniteCyclicPresentation.P2.positiveSelectedChildSideIndex P cut horientation i = ⟨↑i, ⋯⟩
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The target right-child index corresponding to a local child side.
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- LeanEval.Topology.ClassificationOfSurfaces.FiniteCyclicPresentation.P2.positiveRightChildSideIndex P cut horientation i = ⟨↑i, ⋯⟩
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Include the two local child cells into the corresponding two faces of the split pre-realization.
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Send a local child point to its class in the complete split realization.
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The local seam generator is exactly the fresh-edge gluing already present in the target polygonal quotient.
The target quotient map is constant on the complete local child-seam relation.
Include the locally glued pair of P2 children into the complete target realization.
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The selected source face as a map into the split realization #
The positive, nondegenerate selected source face, cut into the two target children and then included in the complete split quotient.
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A selected source side in the left cut piece lands on the exact old side of the selected target child.
A selected source side in the right cut piece lands on the exact old side of the right target child.
The complete forward pre-realization map #
A retained source face differs from its target copy only by a phantom side-count equality.
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Target index corresponding to a side of a retained source face.
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A retained face maps directly to its unchanged target face class.
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Facewise forward map: cut the selected face and retain every other face.
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Continuous forward map on the entire source polygonal pre-realization.
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Transport a source boundary occurrence to the child or retained target face that carries the same old edge after a positive nondegenerate split.
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Exact side-point computation for the complete forward occurrence transport.
The transported occurrence carries exactly the retained old dart.
Distinct source boundary positions remain distinct after routing the selected face between its two P2 children.
Transport an old-edge source pairing to the corresponding pairing of target occurrences.
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Every source gluing generator has equal images under the complete forward P2 map.
The forward pre-map is constant on the complete source gluing relation.
Local inverse maps for the two target children #
Collapse the local child quotient back to the selected source face class.
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Include a point of the actual selected target child into the local child quotient.
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Include a point of the actual right target child into the local child quotient.
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Inverse map on the selected target child.
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Inverse map on the right target child.
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Inverse map on a retained target face.
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Inverse map at an old target-face position, selecting the cut-child inverse exactly at the chosen source face.
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Inverse face map indexed before applying the explicit target faceEquiv.
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Inverse face map on the actual target face type.
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Continuous inverse map on the complete split polygonal pre-realization.
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The inverse pre-map identifies the target's fresh seam for the same local quotient reason used by the forward construction.
On every old boundary side, the inverse pre-map exactly undoes occurrence transport.
Every target boundary occurrence on an old edge is the transported copy of a source occurrence. The two omitted target occurrences are exactly the fresh seam.
Compatible boundary occurrences in a pairing carry the same unoriented edge.
Once source and target occurrences agree, compatibility forces the same parameter direction.
Boundary pairings are determined by their two occurrences and parameter direction.
The two explicitly constructed fresh occurrences exhaust the fresh edge.
A target pairing based at an old edge is exactly the transported pairing of the two corresponding source occurrences.
Occurrence-side form of the exact fresh-seam equality for the inverse pre-map.
The inverse pre-map identifies every target gluing generator: old-edge generators are transported source pairings, while the final edge is the fresh child seam.
The inverse pre-map is constant on the complete target gluing relation.
Forward map after descent through the source polygonal quotient.
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Inverse map after descent through the target polygonal quotient.
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On the locally glued child pair, the descended inverse is the explicit collapse map.
The descended forward map sends the explicit child-collapse class back to the same local child quotient class.
Including a selected-child point in the local child quotient and then in the global quotient is its ordinary polygonal quotient class.
Including a right-child point in the local child quotient and then in the global quotient is its ordinary polygonal quotient class.
The descended inverse is a left inverse on every source pre-realization point.
The descended forward map is a right inverse on every target pre-realization point.
Complete cut-and-paste certificate for a positive, nondegenerate P2 face split.
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Explicit homeomorphism induced by a positive, nondegenerate P2 face split.
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Propositional realization-invariance form for a positive, nondegenerate P2 face split.
Transport across reversal of the chosen cut orientation #
Swap the selected-face position with the fresh right-child position.
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Reversing a cut exchanges its two child faces and fixes every retained face.
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Swapping the two cut pieces exchanges the child faces and fixes every retained face.
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The raw edge relabeling for a swapped cut reverses precisely the fresh edge.
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The raw swapped-cut relabeling at the two split presentations' exact edge types.
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Swapping the two displayed P2 pieces changes only child order and fresh-edge orientation.
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Identity edge relabeling between the definitionally equal edge types of the two reversed-cut splits. Naming the transport keeps the signed-isomorphism boundary proof transparent.
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The split presentations obtained from the two orientations of a cut differ only by swapping the two child faces.
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A negative-orientation nondegenerate cut reduces to the positive theorem after reversing the cut and swapping the two child faces.
Every nondegenerate P2 split preserves the faithful polygonal realization, independently of the chosen traversal orientation.
Every ordinary P2 subdivision preserves the faithful polygonal realization.
For an ordinary-valid source, the exceptional empty-word-sphere alternative in
P2Subdivision is impossible, so the public move relation supplies exactly the two positivity
hypotheses required by the local two-disk gluing model.