We present a layered type theory that integrates three foundational frameworks: Homotopy Type System (HTS), de Rham Cohesive Modal Type Theory (CMTT), and Equivariant Super Type Theory (ESTT). This system builds a progressive structure for formalizing mathematical and physical concepts, from homotopy and higher categorical structures, through geometric cohesion and differential properties, to the rich graded and equivariant world of supergeometry. Inspired by Urs Schreiber’s work on equivariant super homotopy theory, this layered approach offers a modular, type-theoretic foundation for synthetic supergeometry and beyond.
Type theory has emerged as a powerful language for mathematics and physics, unifying computation, logic, and structure. This article introduces a three-layered type theory that extends Martin-Löf’s intensional type theory into a framework capable of capturing homotopy, cohesion, and supergeometry:
Each layer builds on the previous, culminating in a system tailored to
formalize superpoints (ℝᵐ|ⁿ), supersymmetry, and equivariant structures,
as exemplified in Schreiber’s “Equivariant Super Homotopy Theory” (2012).
| 𝖘 A | 𝔾 → A.| ♯ | ℑ | ◯ (four built-in modalities).Tensor and Modalities:
Γ ⊢ A : Uᵢ⁽ᵍ¹⁾, Γ ⊢ B : Uᵢ⁽ᵍ²⁾ → Γ ⊢ ◯ (A ⊗ B) ≃ ◯ A ⊗ ◯ B : Uᵢ⁽⁰⁾
Γ ⊢ A : Uᵢ⁽ᵍ¹⁾, Γ ⊢ B : Uᵢ⁽ᵍ²⁾ → Γ ⊢ ℑ (A ⊗ B) ≃ ℑ A ⊗ ◯ B ⊕ ◯ A ⊗ ℑ B : Uᵢ⁽¹⁾ ⊕ Uᵢ⁽¹⁾
Γ ⊢ 𝖘 (A ⊗ B) ≃ 𝖘 A ⊗ 𝖘 B : Uᵢ⁽ᵍ¹ + ᵍ²⁾
Idempodence:
◯ (◯ (𝖘 ℝ¹|¹)) ≃ ◯ (𝖘 ℝ¹|¹) ≃ ℝ¹.
ℑ (ℑ (𝖘 ℝ¹|¹)) ≃ ℑ (𝖘 ℝ¹|¹) ≃ ℝ⁰|¹.
Projections:
π_◯ : 𝖘 ℝ¹|¹ → ◯ (𝖘 ℝ¹|¹) (x ↦ x).
π_ℑ : 𝖘 ℝ¹|¹ → ℑ (𝖘 ℝ¹|¹) (ψ ↦ ψ).
Tensor:
◯ (𝖘 ℝ¹|¹ ⊗ 𝖘 ℝ¹|¹) ≃ ◯ (𝖘 ℝ¹|¹) ⊗ ◯ (𝖘 ℝ¹|¹) ≃ ℝ¹ ⊗ ℝ¹.
ℑ (𝖘 ℝ¹|¹ ⊗ 𝖘 ℝ¹|¹) ≃ ℝ⁰|¹ ⊗ ℝ¹ ⊕ ℝ¹ ⊗ ℝ⁰|¹ (two odd terms).
Adjuncion:
Hom(◯ (𝖘 ℝ¹|¹), 𝖘 ℝ¹|¹) ≅ Hom(𝖘 ℝ¹|¹, ℑ (𝖘 ℝ¹|¹)) (e.g., maps ℝ¹ → ℝ¹|¹ vs. ℝ¹|¹ → ℝ⁰|¹).
Γ ⊢ Hom(◯ (𝖘 A), 𝖘 B) ≅ Hom(𝖘 A, ℑ (𝖘 B))
Γ ⊢ 𝖘 A : Uᵢ⁽ᵍ⁾ → Γ ⊢ η : 𝖘 A → ℑ (𝖘 A)
Γ ⊢ 𝖘 B : Uᵢ⁽ᵍ⁾ → Γ ⊢ ε : ◯ (𝖘 B) → 𝖘 B
| 𝖘 A | 𝔾 → A.| ♯ | ℑ | ◯ (four built-in modalities).∫ modality:
Γ ⊢ A : Uᵢ⁽ᵍ⁾ → Γ ⊢ ∫ A : Uᵢ⁽ᵍ⁾, ∫ A := Π (X : Uᵢ⁽ᵍ⁾), (♯ X → A) → ♭ X
Γ ⊢ a : A → Γ ⊢ ∫ a : ∫ A, ∫ a := η_∫ a, η_∫ a := λ X. λ f. ♭ (f (η_♯ a))
Γ ⊢ ε_♭ : ∫ (♭ A) → ♭ A
Γ ⊢ Hom(∫ A, B) ≅ Hom(A, ♭ B)
Γ ⊢ ∫ (∫ A) ≃ ∫ A
∇ modality:
Γ ⊢ A : Uᵢ⁽ᵍ⁾ → Γ ⊢ ∇ A : Uᵢ⁽ᵍ⁾, ∇ A := Σ (X : Uᵢ⁽ᵍ⁾), (A → ♭ X) × (♯ X → A)
Γ ⊢ a : A → Γ ⊢ ∇ a : ∇ A, ∇ a := η_∇ a, η_∇ a := (𝟙, λ _ : ♭ 𝟙. ♭ a, λ x : ♯ 𝟙. a)
Γ ⊢ η_♯ : ♯ A → A
Γ ⊢ ε_∇ : ♯ (∇ A) → A
Γ ⊢ ∇ (∇ A) ≃ ∇ A
𝖘 ℝ¹ᴵ¹ lifts ℝ¹ᴵ¹ to a super-context, expected to be isomorphic (𝖘 ℝ¹ᴵ¹ ≃ ℝ¹ᴵ¹), as it’s already a supertype:
Γ ⊢ ℝ¹|¹ : U₀^|0| → Γ ⊢ 𝖘 ℝ¹|¹ : U₀^|0|.
Even part, ◯ (𝖘 ℝ¹|¹) ≃ ℝ¹ (bosonic coordinate space):
Γ ⊢ 𝖘 ℝ¹|¹ : U₀^|0| → Γ ⊢ ◯ (𝖘 ℝ¹|¹) : U₀^|0|.
Odd part, ℑ (𝖘 ℝ¹|¹) ≃ ℝ⁰|¹ (fermionic coordinate):
Γ ⊢ 𝖘 ℝ¹|¹ : U₀^|0| → Γ ⊢ ℑ (𝖘 ℝ¹|¹) : U₀^|1|.
Tensor Product:
Γ ⊢ ◯ (𝖘 ℝ¹|¹ ⊗ 𝖘 ℝ¹|¹) : U₀^|0| ≃ ℝ¹ ⊗ ℝ¹ (even part)
ℑ(𝖘 ℝ¹|¹) ⊗ ◯(𝖘 ℝ¹|¹) ⊕ ◯(𝖘 ℝ¹|¹) ⊗ ℑ(𝖘 ℝ¹|¹) ≃ ℝ⁰|¹ ⊗ ℝ¹ ⊕ ℝ¹ ⊗ ℝ⁰|¹ : U₀^|1| ⊕ U₀^|1|.
Γ ⊢ θ₁ : ℝ^|1|, Γ ⊢ θ₂ : ℝ^|1| → Γ ⊢ θ₁ ⊗ θ₂ = −θ₂ ⊗ θ₁ : ℝ^|1| ⊗ ℝ^|1|
Γ ⊢ θ : ℝ^|1| → Γ ⊢ θ ⊗ θ = 0 : ℝ^|1| ⊗ ℝ^|1|
Γ ⊢ θ₁ : ℝ^|1|, Γ ⊢ θ₂ : ℝ^|1| → Γ ⊢ θ₁ ⊗ θ₂ : ℝ^|1| ⊗ ℝ^|1|
Γ ⊢ θ₁ : ℝ^|1|, Γ ⊢ θ₂ : ℝ^|1| → Γ ⊢ θ₁ ⊗ θ₂ = (−1)^(|1| |1|) θ₂ ⊗ θ₁ : ℝ^|1| ⊗ ℝ^|1|
Γ ⊢ θ₁ ⊗ θ₂ = −θ₂ ⊗ θ₁ : ℝ^|1| ⊗ ℝ^|1|
Γ ⊢ θ₁ ⊗ θ₂ = (−1)^(|1| |1|) θ₂ ⊗ θ₁ = −θ₂ ⊗ θ₁ : ℝ^|1| ⊗
Γ ⊢ ℝ^|0| : Uᵢ^|0|
Γ ⊢ ℝ^|1| : Uᵢ^|1|
Γ ⊢ ℝ^|0| ⊗ ℝ^|1| : Uᵢ^|1|
|0| + |1| = |1|
Γ ⊢ x : ℝ^|0| Γ ⊢ θ : ℝ^|1| Γ ⊢ x ⊗ θ : ℝ^|0| ⊗ ℝ^|1|
Γ ⊢ g : G → Γ ⊢ t g : ℝ^|0| ⊗ ℝ^|1| ⊗ ℝ^|1|
⊢ Γ, g : G, a : ℝ^|0| ⊗ ℝ^|1| ⊗ ℝ^|1| → Γ
⊢ λg.a : G → ℝ^|0| ⊗ ℝ^|1| ⊗ ℝ^|1|
⊢ t : G → ℝ^|0| ⊗ ℝ^|1| ⊗ ℝ^|1|
Fibonacci Anions:
def FibAnyon : Type_{lin} := 1 + τ
def FibState (c : Config) : Type_{lin} := Σ (a : FibAnyon), KUᶿ(c; ℂ)
def FibFusionRule : FibAnyon → FibAnyon → Type_{lin}
def FibFusionRule (1 a : FibAnyon) := Id_{FibAnyon}(a, a)
def FibFusionRule (τ τ : FibAnyon) := 1 + τ
def fuseFib (a b: FibAnyon) : Type := Σ (c: FibAnyon), FibFusionRule a b
def fuseFib (τ τ: FibAnyon) : Type ≡ (c, proof) where c : 1 + τ, proof : Id_{FibAnyon}(c, 1 + τ)
def fuseFibState (s₁ s₂ : FibState c) : FibState c := \ (a₁, q₁) (a₂, q₂), (c, fuseQubit(q₁, q₂, c))
def measureFib : Σ(c : FibAnyon).FibFusionRule a b → FibState Config := (c, qubit_c)
def τ₁ : FibAnyon :≡ τ
def τ₂ : FibAnyon :≡ τ
def s₁ : FibState c :≡ (τ₁, q₁)
def s₂ : FibState c :≡ (τ₂, q₂)
def fused : Σ(c : FibAnyon), FibFusionRule τ τ :≡ fuseFib τ₁ τ₂
def resolved : FibState c :≡ measureFib fused
Fusion for su(2) k-Anyonic States:
def j₀ : Su2Anyon 2 :≡ 0
def j₁ : Su2Anyon 2 :≡ 1/2
def state : Su2State c 2 :≡ (j₁, qubit)
def braid 2 j₁ j₁ : KU^\tau_G(c; ℂ)
def Su2Anyon : ℕ → Type_{lin}
def Su2Anyon k :≡ { j : ℝ | 0 ≤ j ≤ k/2 ∧ 2j ∈ ℕ }
def Su2FusionRule : ℕ → Su2Anyon k → Su2Anyon k → Type
def Su2FusionRule k j₁ j₂ ≡ Σ(j : Su2Anyon k).(|j₁ - j₂| ≤ j ≤ min(j₁ + j₂, k - j₁ - j₂))
def braid (k : ℕ) (a b : Su2Anyon k) : KU^\tau_G(Config; ℂ)
def braid k a b :≡ R_{ab} · state(a, b)
def fuseSu2State (k : ℕ) (s₁ s₂ : Su2State c k) : Su2State c k
def fuseSu2State k (j₁, q₁) (j₂, q₂) :≡ (j, fuseQubit(q₁, q₂, j))
def fuse (k : ℕ) (j₁ j₂ : Su2Anyon k) := Σ(j : Su2Anyon k), Id_{Su2Anyon k}(j, fuseRule(j₁, j₂))
def fuse k j₁ j₂ :≡ (j, proof) where j ∈ {|j₁ - j₂|, ..., min(j₁ + j₂, k - j₁ - j₂)}
def fuseSu2 (k : ℕ)(j₁ j₂ : Su2Anyon k) : Su2FusionRule k j₁ j₂
def fuseSu2 k j₁ j₂ :≡ (j, proof)
where j = choose(|j₁ - j₂|, min(j₁ + j₂, k - j₁ - j₂)),
proof : Id_{Su2Anyon k}(j, fusionTerm(j₁, j₂))
Majorana Zero Modes:
def MZM : Type_{lin} := γ
def MZMState (c: Config) : Type_{lin} := Σ(m : MZM), KU¹(c; ℂ)
def fuseMZM (m₁ m₂ : MZM) := Σ (c : FibAnyon), MZMFusionRule m₁ m₂
def fuseMZM (γ γ : MZM) ≡ (1, refl)
def resolveMZM : Σ(c : FibAnyon), MZMFusionRule γ γ → FibState Config
def resolveMZM (1, refl) ≡ (1, qubit_1)
def fuseMZMState (s₁ s₂ : MZMState c) : FibState c := \ (γ, q₁) (γ, q₂), (1, fuseQubit(q₁, q₂, 1))