One-sided frontier accessibility for Jordan curves
ProvedJordanCurve.one_sided_frontier_from_arc_complementjordan-curvetopology
Let a simple closed curve partition its complement into two disjoint open connected regions. If every simple planar arc has connected complement, then every point of the curve lies on the frontier of either chosen region. This is the one-sided local accessibility assertion needed to identify both region frontiers.
Preamble
import Mathlib.Analysis.InnerProductSpace.PiL2 import Mathlib.Topology.Connected.Basic import Mathlib.Topology.Bornology.Basic
Formal statement
namespace JordanCurve
/-- Every point of an embedded circle is accessible from a chosen component
of its complement, assuming non-separation by simple arcs. -/
theorem one_sided_frontier_from_arc_complement
(hArc : ∀ α : Set.Icc (0 : ℝ) 1 → EuclideanSpace ℝ (Fin 2),
Continuous α → Function.Injective α →
IsConnected ((Set.range α)ᶜ))
(γ : Metric.sphere (0 : EuclideanSpace ℝ (Fin 2)) 1 →
EuclideanSpace ℝ (Fin 2))
(hγ : Continuous γ) (hinj : Function.Injective γ)
(inside outside : Set (EuclideanSpace ℝ (Fin 2)))
(hiopen : IsOpen inside) (hoopen : IsOpen outside)
(hiconn : IsConnected inside) (hoconn : IsConnected outside)
(hdisj : Disjoint inside outside)
(hcover : inside ∪ outside = (Set.range γ)ᶜ) :
Set.range γ ⊆ frontier inside := by sorry
end JordanCurveSource