Rectangles, crossings, annuli and the box-crossing property on ℤ²

DefinitionInteger rectangle in the plane lattice#✓fully proved

The rectangle [a, b] × [c, d] in ℤ².

def rect (a b c d : ℤ) : Set (Site 2) :=
  {x | a ≤ x 0 ∧ x 0 ≤ b ∧ c ≤ x 1 ∧ x 1 ≤ d}
Uses 1 · Used by 29

TheoremMeasurability of connection inside a set#✓fully proved

The event that two vertices are connected by an open path inside S is measurable.

theorem measurableSet_connectedWithin {d : ℕ} (S : Set (Site d)) (x y : S) :
    MeasurableSet {ω : ConfigSpace (Sym2 (Site d)) | ConnectedWithin d ω S x y}
Uses 6 · Used by 5

DefinitionLeft side of a general lattice rectangle#✓fully proved

The left side {a} × [c, d] of rect a b c d.

def leftSide (a b c d : ℤ) : Set (Site 2) := {x | x ∈ rect a b c d ∧ x 0 = a}
Uses 2 · Used by 6

DefinitionRight side of a general lattice rectangle#✓fully proved

The right side {b} × [c, d] of rect a b c d.

def rightSide (a b c d : ℤ) : Set (Site 2) := {x | x ∈ rect a b c d ∧ x 0 = b}
Uses 2 · Used by 6

DefinitionBottom side of a general lattice rectangle#✓fully proved

The bottom side [a, b] × {c} of rect a b c d.

def bottomSide (a b c d : ℤ) : Set (Site 2) := {x | x ∈ rect a b c d ∧ x 1 = c}
Uses 2 · Used by 7

DefinitionTop side of a general lattice rectangle#✓fully proved

The top side [a, b] × {d} of rect a b c d.

def topSide (a b c d : ℤ) : Set (Site 2) := {x | x ∈ rect a b c d ∧ x 1 = d}
Uses 2 · Used by 7

DefinitionOpen left–right crossing of a general rectangle#✓fully proved

An open left–right crossing of rect a b c d by a path inside the rectangle.

def HorizontalCrossing (ω : ConfigSpace (Sym2 (Site 2))) (a b c d : ℤ) : Prop :=
  ∃ (x : leftSide a b c d) (y : rightSide a b c d),
    ConnectedWithin 2 ω (rect a b c d)
      ⟨(x : Site 2), leftSide_subset x.2⟩ ⟨(y : Site 2), rightSide_subset y.2⟩
Uses 6 · Used by 4

DefinitionOpen bottom–top crossing of a general rectangle#✓fully proved

An open bottom–top crossing of rect a b c d by a path inside the rectangle.

def VerticalCrossing (ω : ConfigSpace (Sym2 (Site 2))) (a b c d : ℤ) : Prop :=
  ∃ (x : bottomSide a b c d) (y : topSide a b c d),
    ConnectedWithin 2 ω (rect a b c d)
      ⟨(x : Site 2), bottomSide_subset x.2⟩ ⟨(y : Site 2), topSide_subset y.2⟩
Uses 6 · Used by 4

DefinitionLeft–right crossing event of a general rectangle#✓fully proved

The event that rect a b c d has an open left–right crossing.

def horizontalCrossingEvent (a b c d : ℤ) : Set (ConfigSpace (Sym2 (Site 2))) :=
  {ω | HorizontalCrossing ω a b c d}
Uses 3 · Used by 3

DefinitionBottom–top crossing event of a general rectangle#✓fully proved

The event that rect a b c d has an open bottom–top crossing.

def verticalCrossingEvent (a b c d : ℤ) : Set (ConfigSpace (Sym2 (Site 2))) :=
  {ω | VerticalCrossing ω a b c d}
Uses 3 · Used by 2

TheoremMeasurability of the left–right crossing event#✓fully proved

A left–right crossing event of a rectangle is measurable.

theorem measurableSet_horizontalCrossingEvent (a b c d : ℤ) :
    MeasurableSet (horizontalCrossingEvent a b c d)
Uses 8 · Used by 1

TheoremMeasurability of the bottom–top crossing event#✓fully proved

A bottom–top crossing event of a rectangle is measurable.

theorem measurableSet_verticalCrossingEvent (a b c d : ℤ) :
    MeasurableSet (verticalCrossingEvent a b c d)
Uses 8 · Used by 1

DefinitionDual left–right crossing of a rectangle#✓fully proved

A left–right crossing of rect a b c d in the dual configuration dualConfig ω (an open crossing of the dual lattice, read through the primal coordinates of dualConfig).

def DualHorizontalCrossing (ω : ConfigSpace (Sym2 (Site 2))) (a b c d : ℤ) : Prop :=
  HorizontalCrossing (dualConfig ω) a b c d
Uses 4 · Used by 1

DefinitionDual bottom–top crossing of a rectangle#✓fully proved

A bottom–top crossing of rect a b c d in the dual configuration dualConfig ω.

def DualVerticalCrossing (ω : ConfigSpace (Sym2 (Site 2))) (a b c d : ℤ) : Prop :=
  VerticalCrossing (dualConfig ω) a b c d
Uses 4 · Used by 1

DefinitionDual left–right crossing event#✓fully proved

The event DualHorizontalCrossing.

def dualHorizontalCrossingEvent (a b c d : ℤ) : Set (ConfigSpace (Sym2 (Site 2))) :=
  {ω | DualHorizontalCrossing ω a b c d}
Uses 3

DefinitionDual bottom–top crossing event#✓fully proved

The event DualVerticalCrossing.

def dualVerticalCrossingEvent (a b c d : ℤ) : Set (ConfigSpace (Sym2 (Site 2))) :=
  {ω | DualVerticalCrossing ω a b c d}
Uses 3

DefinitionSquare annulus in the plane lattice#✓fully proved

The annulus z + (Λ_{2n} \ Λ_n), where Λ_n = [-n, n]².

def annulus (z : Site 2) (n : ℕ) : Set (Site 2) :=
  (fun x => z + x) '' (box 2 (2 * n) \ box 2 n)
Uses 2 · Used by 1

DefinitionOpen circuit lying in an annulus#✓fully proved

The closed walk w is an open circuit all of whose vertices lie in annulus z n.

def IsAnnulusCircuit (ω : ConfigSpace (Sym2 (Site 2))) (z : Site 2) (n : ℕ)
    {v : Site 2} (w : (openSubgraph 2 ω).Walk v v) : Prop :=
  IsOpenCircuit 2 ω w ∧ ∀ u ∈ w.support, u ∈ annulus z n
Uses 5 · Used by 1

DefinitionExistence of an open circuit in an annulus#✓fully proved

There is an open circuit inside annulus z n.

def AnnulusCircuit (ω : ConfigSpace (Sym2 (Site 2))) (z : Site 2) (n : ℕ) : Prop :=
  ∃ (v : Site 2) (w : (openSubgraph 2 ω).Walk v v), IsAnnulusCircuit ω z n w
Uses 4 · Used by 2

DefinitionOpen circuit event in an annulus#✓fully proved

The event AnnulusCircuit.

def annulusCircuitEvent (z : Site 2) (n : ℕ) : Set (ConfigSpace (Sym2 (Site 2))) :=
  {ω | AnnulusCircuit ω z n}
Uses 3

DefinitionOpen circuit in an annulus centered at the origin#✓fully proved

There is an open circuit inside the annulus Λ_{2n} \ Λ_n centered at the origin.

def AnnulusCircuit0 (ω : ConfigSpace (Sym2 (Site 2))) (n : ℕ) : Prop :=
  AnnulusCircuit ω (fun _ => 0) n
Uses 3

DefinitionLeft–right crossing event of a box with given aspect ratio#✓fully proved

The left–right open crossing of the box [0, ⌊αn⌋] × [0, n] (aspect ratio α).

noncomputable def boxCrossingEvent (α : ℝ) (n : ℕ) :
    Set (ConfigSpace (Sym2 (Site 2))) :=
  horizontalCrossingEvent 0 (⌊α * n⌋.toNat) 0 n
Uses 3 · Used by 3

DefinitionBox-crossing property for a sequence of measures#✓fully proved

The box-crossing property for a sequence of set functions μ n: for every aspect ratio α > 0 there is c > 0 with μ n (boxCrossingEvent α n) ≥ c for all n.

def P5 (μ : ℕ → Set (ConfigSpace (Sym2 (Site 2))) → ℝ) : Prop :=
  ∀ α : ℝ, 0 < α → ∃ c : ℝ, 0 < c ∧ ∀ n : ℕ, c ≤ μ n (boxCrossingEvent α n)
Uses 3 · Used by 1

DefinitionUniform two-sided box-crossing property#✓fully proved

The uniform two-sided box-crossing property for a family μ ξ n: for every α > 0 there is c > 0 with c ≤ μ ξ n (boxCrossingEvent α n) ≤ 1 - c for all ξ and n.

def P5c {Ξ : Type*} (μ : Ξ → ℕ → Set (ConfigSpace (Sym2 (Site 2))) → ℝ) : Prop :=
  ∀ α : ℝ, 0 < α → ∃ c : ℝ, 0 < c ∧ ∀ (ξ : Ξ) (n : ℕ),
    c ≤ μ ξ n (boxCrossingEvent α n) ∧ μ ξ n (boxCrossingEvent α n) ≤ 1 - c
Uses 3
24 fully proved

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