Documentation

LeanPool.ClassificationOfSurfaces.FiniteCyclicP1Realization

Polygonal realization of Gallier--Xu P1 #

The boundary of every source face is assigned weight two at occurrences of the subdivided edge and weight one everywhere else. WeightedCircle turns those weights into the exact boundary homeomorphism required by P1, and radial extension gives the corresponding disk homeomorphism.

The P1 subdivision weights around one face boundary.

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    The first target side replacing source side i.

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      Transport a source occurrence to the first target occurrence in its expanded block.

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        More generally, lookup inside an expanded block agrees with lookup in the substituted dart-word.

        @[reducible, inline]

        A position in the concatenation of blocks whose lengths are weights.

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          @[simp]

          Distinct block-local positions have distinct linear positions.

          A target-side index inside the expanded block of source side i.

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            @[reducible, inline]

            A source occurrence together with one of the one or two target sides replacing it.

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              Transport a block-local source position to its target boundary occurrence.

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                The target edge at a block-local offset.

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                  Each target subedge has the same boundary/internal status as its source edge.

                  A selected source side has a second local target-side offset.

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                    Reversing a source dart reverses the expanded block and flips its signed darts.

                    Transport a block-local offset across an equal-dart pairing.

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                      Transport a block-local offset across a flipped-dart pairing.

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                        Each same-direction old pairing expands to corresponding target-subedge pairings.

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                          Each opposite-direction old pairing expands to reversed target-subedge pairings.

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                            The second target side replacing a selected source occurrence.

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                              Transport a selected source occurrence to the second occurrence in its expanded block.

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                                The exact weighted homeomorphism between the source and P1-expanded face boundaries.

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                                  Radially extend the weighted boundary map to the whole face disk.

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                                    P1 acts facewise on the polygonal pre-realization.

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                                      Exact boundary-coordinate formula for the facewise P1 map.

                                      @[simp]
                                      theorem LeanEval.Topology.ClassificationOfSurfaces.FiniteCyclicPresentation.P1.samePairedOffset_val {P : FiniteCyclicPresentation} (a : P.Edge) (pairing : P.BoundaryPairing) (hcompatible : pairing.target.dart = pairing.source.dart) (k : Fin (dartWeight a pairing.source.dart)) :
                                      (samePairedOffset a pairing hcompatible k) = k

                                      Expanded source blocks enumerate all target boundary occurrences.

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                                        Every target pairing is one of the subedge pairings expanded from a unique old pairing.

                                        Convert a target subedge-local parameter back to the original source-side parameter.

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                                          Descent to the faithful polygonal quotient #

                                          Canonical P1 expansion preserves the faithful polygonal realization.

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                                            Propositional realization-invariance form for the canonical P1 expansion.

                                            Every P1 subdivision, including signed relabeling of the canonical target, preserves the faithful polygonal realization.