import Mathlib.Analysis.InnerProductSpace.Adjoint
import Mathlib.Analysis.InnerProductSpace.Basic
import Mathlib.Analysis.Normed.Group.Basic
import Mathlib.Algebra.Order.Field.Basic

noncomputable section

open InnerProductSpace

namespace QFD

variable {H : Type*} [NormedAddCommGroup H] [InnerProductSpace ℝ H] [CompleteSpace H]

/-!
## 1. Geometric Operators
We define the structure of the operators governing the QFD soliton.
-/

/-- The internal rotation generator `J`. It corresponds to a physical bivector.
    Property: It must be Skew-Adjoint (J† = -J). -/
structure BivectorGenerator (H : Type*) [NormedAddCommGroup H]
    [InnerProductSpace ℝ H] [CompleteSpace H] where
  op : H →L[ℝ] H
  skew_adj : ContinuousLinearMap.adjoint op = -op

/-- The stability operator `L` (Hessian of Energy). Must be Self-Adjoint. -/
structure StabilityOperator (H : Type*) [NormedAddCommGroup H]
    [InnerProductSpace ℝ H] [CompleteSpace H] where
  op : H →L[ℝ] H
  self_adj : ContinuousLinearMap.adjoint op = op

variable (J : BivectorGenerator H)
variable (L : StabilityOperator H)

/-!
## 2. Derived Geometric Structures
-/

/-- The Casimir Operator (Geometric Spin Squared): C = -J² = J†J -/
def CasimirOperator : H →L[ℝ] H :=
  -(J.op ∘L J.op)

/--
The Symmetric Sector (Spacetime): States with zero internal spin (Kernel of C).
-/
def H_sym : Submodule ℝ H :=
  LinearMap.ker (CasimirOperator J)

/--
The Orthogonal Sector (Extra Dimensions): States orthogonal to the symmetric sector.
-/
def H_orth : Submodule ℝ H :=
  (H_sym J).orthogonal

/-!
## 3. The Structural Theorems (Axioms of the Soliton)
We explicitly state the properties required of the physical vacuum.
-/

/-- Hypothesis 1: Topological Quantization.
    Non-zero winding modes have at least unit geometric angular momentum. -/
def HasQuantizedTopology (J : BivectorGenerator H) : Prop :=
  ∀ x ∈ H_orth J, @inner ℝ H _ (x : H) (CasimirOperator J x) ≥ ‖x‖^2

/-- Hypothesis 2: Energy Dominance (The Centrifugal Barrier).
    The energy cost of stabilizing the particle (L) dominates the
    angular momentum (C). -/
def HasCentrifugalBarrier (L : StabilityOperator H) (J : BivectorGenerator H)
    (barrier : ℝ) : Prop :=
  ∀ x : H, @inner ℝ H _ x (L.op x) ≥ barrier * @inner ℝ H _ x (CasimirOperator J x)

/-!
## 4. The Spectral Gap Theorem
Proof that 4D emergence is necessary if the barrier is positive.
-/

theorem spectral_gap_theorem
  (barrier : ℝ)
  (h_pos : barrier > 0)
  (h_quant : HasQuantizedTopology J)
  (h_dom : HasCentrifugalBarrier L J barrier) :
  ∃ ΔE > 0, ∀ η ∈ H_orth J, @inner ℝ H _ (η : H) (L.op η) ≥ ΔE * ‖η‖^2 := by
  -- We claim the gap ΔE is exactly the barrier strength
  use barrier
  constructor
  -- 1. Proof that Gap > 0
  · exact h_pos
  -- 2. Proof of the Energy Inequality
  · intro η h_eta_orth
    -- Retrieve specific inequalities for this state η
    have step1 : @inner ℝ H _ (η : H) (L.op η) ≥
        barrier * @inner ℝ H _ (η : H) (CasimirOperator J η) :=
      h_dom η
    have step2 : @inner ℝ H _ (η : H) (CasimirOperator J η) ≥ ‖η‖^2 :=
      h_quant η h_eta_orth
    -- Chain the logic using `calc` for rigor
    calc @inner ℝ H _ (η : H) (L.op η)
      _ ≥ barrier * @inner ℝ H _ (η : H) (CasimirOperator J η) := step1
      _ ≥ barrier * (1 * ‖η‖^2) := by
          -- Multiply inequality step2 by positive barrier
          rw [one_mul]
          apply mul_le_mul_of_nonneg_left step2 (le_of_lt h_pos)
      _ = barrier * ‖η‖^2 := by ring

end QFD