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LeanPool.ClassificationOfSurfaces.FiniteCyclicMoves

Finite cyclic move closures #

This file combines signed presentation isomorphisms and the two primitive Gallier--Xu subdivisions into stable closure APIs.

Subdivides is the directed reflexive-transitive closure. It preserves ordinary validity, connectivity, and Gallier validity. HasCommonSubdivision P Q supplies a validity-safe common target for topological comparison: starting with two ordinary-valid presentations, both forward chains remain ordinary-valid. This is stronger operational data than an unrestricted symmetric move chain, which may pass through the exceptional empty-word sphere where PolygonalRealization is deliberately unavailable.

MoveEquivalent is also provided as the purely syntactic equivalence closure. A common subdivision implies move equivalence, but no converse or confluence theorem is asserted here.

One directed presentation step: a signed isomorphism, P1 subdivision, or P2 subdivision.

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    Every directed step preserves ordinary surface incidence validity.

    Every directed step preserves face-incidence connectivity.

    Every directed step preserves the packed Gallier--Xu validity predicate.

    Directed subdivision chains preserve ordinary surface incidence validity.

    Directed subdivision chains preserve face-incidence connectivity.

    Every directed subdivision chain is a syntactic move equivalence.

    The stable proof obligation for primitive realization invariance.

    The P1 and P2 realization files discharge the corresponding disjuncts; signed isomorphisms are already implemented by SignedPresentationIso.polygonallyEquivalent.

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      The realization-invariance obligation isolated to P1 subdivisions.

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        The realization-invariance obligation isolated to P2 subdivisions.

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          Signed-isomorphism invariance plus the two primitive geometric obligations supplies invariance for every directed elementary step.

          If every primitive directed step preserves the faithful polygonal quotient, so does every directed subdivision chain.

          Primitive realization invariance promotes a common-subdivision certificate to a homeomorphism of faithful polygonal quotients.