A square model for polygon cells #
This file supplies the geometric cut-and-paste model used by Gallier--Xu P2. The closed unit
square is treated as a convex disk. Its boundary is parameterized explicitly by radial
projection of the Euclidean circle, and an arbitrary homeomorphism from the circle to the
frontier of a bounded convex disk is extended across PolygonCell.
The centered closed unit square.
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The geometric boundary of the centered square.
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Radial projection of a nonzero point to the square boundary.
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The radial homeomorphism from the Euclidean unit circle to the centered square boundary.
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Extending a chosen square-boundary parameterization #
A fixed ambient straightening of the centered square to the Euclidean unit disk.
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Restrict the fixed ambient straightening to the closed square.
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The fixed square straightening restricted to its frontier.
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Extend any selected parameterization of the square frontier across a polygon cell.
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A distinguished polygon side on the right side of the square #
Boundary weights for a polygon whose final side is distinguished.
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Boundary weights for a polygon whose first side is distinguished.
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Rotate the circle counterclockwise by π / 4.
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Put the first side of an (r+1)-gon on the same square side, but with reversed traversal.
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The two fresh sides have exactly the same point of the local square after reversing the right-child parameter.
Square model for the selected child of a nondegenerate P2 split.
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Square model for the right child of a nondegenerate P2 split.
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The distinguished final side covers every point of the local square's right edge.
The distinguished first side covers every point of the local square's right edge.
Gluing two square models along their right sides #
Gluing two square disks along their distinguished sides #
The disjoint union of the two local square disks.
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The generating seam relation: the right side of the left local square is glued, point for point, to the right side of the horizontally reflected right local square.
- glue (z w : ↑square) (hz : (↑z).re = 1) (hw : (↑w).re = 1) (him : (↑z).im = (↑w).im) : SeamGenerator (Sum.inl z) (Sum.inr w)
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The equivalence relation generated by the common side of the two square disks.
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The topological quotient obtained by gluing the two local square disks along the seam.
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Merge the two local squares into the left and right halves of one outer square.
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The merge map is constant on the equivalence closure of the seam relation.
Equality between opposite merged summands can only occur on the declared seam.
No identifications are hidden by the planar merge: equality after merging is exactly generated by equality inside one summand and the declared seam relation.
The continuous map induced on the quotient by merging the two local squares.
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Gluing two square disks along the selected sides is again a closed disk.
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Transporting the seam model to two nondegenerate polygon cells #
The two polygon cells occurring in a nondegenerate, positively oriented P2 split.
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The geometric seam relation on the two child cells, expressed through their square models. This formulation records the entire common edge and is convenient for quotient-kernel arguments.
- glue {l r : ℕ} {hl : 0 < l} {hr : 0 < r} (z : PolygonCell (l + 1)) (w : PolygonCell (r + 1)) (hz : (↑((finalSideCellHomeomorph l hl) z)).re = 1) (hw : (↑((firstSideCellHomeomorph r hr) w)).re = 1) (him : (↑((finalSideCellHomeomorph l hl) z)).im = (↑((firstSideCellHomeomorph r hr) w)).im) : ChildSeamGenerator l r hl hr (Sum.inl z) (Sum.inr w)
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The equivalence relation generated by identifying the two child-cell seam edges.
The setoid generated by identifying the two child-cell seam edges.
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The quotient of the two child polygon cells by their complete common side.
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Straighten both P2 child cells simultaneously to their local square models.
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The simultaneous child straightening identifies exactly the two generated seam relations.
The actual two-child polygon quotient of a nondegenerate P2 cut is a closed disk.
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A marked side of a polygon with at least two sides has no parameter self-overlap.
The parameter-level fresh-edge identification used by a positive P2 split.
- glue {l r : ℕ} (t : ↑unitInterval) : ParamChildSeamGenerator l r (Sum.inl ((PolygonCell.side (Fin.last l)) t)) (Sum.inr ((PolygonCell.side 0) (unitInterval.symm t)))
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The square-model seam is exactly the equivalence closure of the fresh-side parameter map.
The parameter-independent seam equivalence relation used by the quotient comparison.
The setoid used by the parameter-independent quotient comparison.
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The quotient of the parameterized child pair by its seam relation.
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Two nondegenerate P2 child polygons, glued by the precise reversed fresh-edge parameter, form a closed disk.
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The external boundary arcs of the glued child disk #
The old-boundary arc of the selected child, before placing its square on the left.
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The old-boundary arc of the right child, before its horizontal reflection.
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The right child's old boundary, reflected and placed on the outer square frontier.
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The outer boundary assembled from the two old-boundary arcs #
A continuous coordinate, from 0 to 3, along the left half of the square boundary.
It starts at the midpoint of the top edge, passes the two left corners, and ends at the
midpoint of the bottom edge.
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The analogous coordinate on the right half, oriented from bottom to top.
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Clip a parameter for the combined outer boundary to the left child's old arc.
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Clip and translate a combined parameter to the right child's old arc.
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The full outer boundary path: the selected child's old sides followed by the right child's old sides. Its two endpoints both map to the top midpoint.
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Remove the syntactic leading zero from the endpoint interval used by AddCircle.
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The outer path with the syntactic endpoint interval used by AddCircle.EndpointIdent.
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The additive circle parameterized by the old sides is the outer square boundary.
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The exact boundary parameterization used to extend the old sides across the selected source polygon.
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The combined real parameter of a polygon side.
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The same parameter with the split side count displayed as a sum in ℝ.
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- LeanEval.Topology.ClassificationOfSurfaces.DiskSquare.sourceSideParameter l r i t = ⟨↑↑i + ↑t, ⋯⟩
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Extend the exact outer-boundary parameterization across the unsplit source polygon.
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On every old left side, the unsplit source polygon map agrees exactly with the corresponding placed child side.
On every old right side, the unsplit source polygon map agrees exactly with the corresponding reflected and placed child side.
The complete local P2 equivalence: one unsplit polygon is homeomorphic to the quotient of the two child polygons by their reversed fresh-side identification.
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The local P2 homeomorphism sends every left source side to the corresponding selected-child side class.
The local P2 homeomorphism sends every right source side to the corresponding right-child side class.