Documentation

LeanPool.ClassificationOfSurfaces.FiniteCyclicUnorientedRealization

Polygonal realization under independently reoriented faces #

Gallier--Xu treat a face and the same face read in the opposite direction interchangeably. This file records that convention explicitly. An UnorientedPresentationIso may rename and reorient edges, relabel faces, cyclically rotate their boundaries, and independently reverse the traversal orientation of every face.

Unlike SignedPresentationIso, this broader comparison does not claim to preserve the current orientation-sensitive IsSurfaceValid predicate. When both endpoints are ordinarily valid, it does preserve their faithful polygonal realizations. This is the exact extra comparison needed by the cross-cap pseudo-rewrite, whose common P2 refinement reads one of its two faces backwards.

Reflection of a polygon cell across the real axis.

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    Reflection reverses both the cyclic side index and its interval parameter.

    Presentation isomorphism up to independent choices of traversal orientation on target faces.

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      Ordinary signed presentation isomorphisms are the orientation-preserving special case.

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        Face adjacency is preserved when target faces may be read in either orientation.

        Face-incidence connectivity is preserved by an unoriented presentation isomorphism.

        Looking up the reversed signed word reverses the finite index and flips the dart.

        The target-boundary rotation selected for an unoriented presentation isomorphism.

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          @[reducible, inline]

          The side index in the chosen orientation of the target face.

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            @[reducible, inline]

            Convert an oriented target-side index to the stored boundary indexing.

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              Reflection reverses the side parameter exactly when the target face is read backwards.

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                The rotated oriented target side carries the relabeled source dart.

                The stored target occurrence carries the relabeled dart, flipped exactly when its face was read backwards.

                The facewise disk homeomorphism: rotate to the selected cyclic spelling, then reflect if the target face is read backwards.

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                  The facewise homeomorphism sends a source side to the corresponding stored target side, with the interval parameter reversed exactly for a reversed face.

                  Transport a boundary occurrence through the selected cyclic rotation and possible reflection.

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                    On a labelled side, the pre-realization map performs its selected cyclic shift and possible reflection.

                    Ignoring the selected cyclic shifts and reflections, the occurrence types have equal cardinality.

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                      Toggle a gluing direction when exactly one incident face is reflected.

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                        The transported gluing parameter commutes with the two optional side reflections.

                        Transport a compatible source pairing, toggling its parameter direction precisely when one of the two incident faces is reflected.

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                          Pull a compatible target pairing back through the occurrence equivalence.

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                            Independent edge and face reorientation preserves the faithful polygonal realization whenever both endpoint presentations satisfy ordinary incidence validity.

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                              Propositional realization-invariance form for face-reversing presentation comparisons.