Research-Stack/0-Core-Formalism/lean/Semantics/Semantics/BraidedFieldPaths.lean
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import Mathlib.Data.List.Basic
import Mathlib.Logic.Equiv.Basic
import Semantics.BraidedField
/-!
# Braided Field Sets & Virtual Information Paths
This module formalizes the topology of virtual information paths
created by braiding polaron-polariton quasiparticles (anyons).
Instead of tracking particle locations in Cartesian space, information
is stored in the topological equivalence class of the braid sequence.
This is a finite braid-word scaffold. It does not prove physical topological
protection, material feasibility, or local-noise immunity.
-/
namespace Semantics.BraidedField
/--
A single generator `σ_i` representing the virtual operation of
swapping adjacent quasiparticles `i` and `i+1` in a 2D manifold.
-/
structure Swap (n : Nat) where
i : Nat
valid : i + 1 < n
deriving Repr, DecidableEq
/--
A Virtual Information Path is a temporal sequence of swaps.
In formal topology, this is known as a braid word.
This acts as an encoding system where data is written into spacetime history.
-/
abbrev VirtualPath (n : Nat) := List (Swap n)
/--
Topological equivalence of virtual paths.
Two paths are treated as the same candidate path if they can be deformed into
one another via the Artin braid relations. This is a structural equivalence
relation for the virtual-path model, not a physical immunity claim.
-/
inductive TopologicallyEquivalent {n : Nat} : VirtualPath n → VirtualPath n → Prop where
| refl (p : VirtualPath n) : TopologicallyEquivalent p p
| symm {p q : VirtualPath n} :
TopologicallyEquivalent p q → TopologicallyEquivalent q p
| trans {p q r : VirtualPath n} :
TopologicallyEquivalent p q → TopologicallyEquivalent q r → TopologicallyEquivalent p r
/--
Far-commutation: Swapping particles on opposite sides of the field
are independent operations. (σ_i σ_j = σ_j σ_i if |i - j| ≥ 2)
-/
| commute (i j : Swap n) (left right : VirtualPath n)
(h_dist : i.i + 1 < j.i j.i + 1 < i.i) :
TopologicallyEquivalent (left ++ [i, j] ++ right) (left ++ [j, i] ++ right)
/--
The Yang-Baxter Equation / braid relation.
The core braid-word equivalence of the virtual-path encoding system.
(σ_i σ_{i+1} σ_i = σ_{i+1} σ_i σ_{i+1})
-/
| braid_rel (i j : Swap n) (left right : VirtualPath n)
(h_adj : j.i = i.i + 1) :
TopologicallyEquivalent (left ++ [i, j, i] ++ right) (left ++ [j, i, j] ++ right)
/--
A basic theorem demonstrating that the relation is explicitly symmetric.
-/
theorem path_integrity_preserved {n : Nat} (p1 p2 : VirtualPath n)
(h : TopologicallyEquivalent p1 p2) :
TopologicallyEquivalent p2 p1 := by
exact TopologicallyEquivalent.symm h
namespace Examples
def s0 : Swap 4 := ⟨0, by decide⟩
def s1 : Swap 4 := ⟨1, by decide⟩
def s2 : Swap 4 := ⟨2, by decide⟩
def farLeft : VirtualPath 4 := [s0, s2]
def farRight : VirtualPath 4 := [s2, s0]
def yangBaxterLeft : VirtualPath 4 := [s0, s1, s0]
def yangBaxterRight : VirtualPath 4 := [s1, s0, s1]
def pathLength {n : Nat} (p : VirtualPath n) : Nat :=
p.length
def generatorIndexSum {n : Nat} (p : VirtualPath n) : Nat :=
p.foldl (fun acc swap => acc + swap.i) 0
theorem far_commute_example : TopologicallyEquivalent farLeft farRight := by
exact TopologicallyEquivalent.commute s0 s2 [] [] (by decide)
theorem yang_baxter_example : TopologicallyEquivalent yangBaxterLeft yangBaxterRight := by
exact TopologicallyEquivalent.braid_rel s0 s1 [] [] (by decide)
theorem far_commute_symmetric : TopologicallyEquivalent farRight farLeft := by
exact path_integrity_preserved farLeft farRight far_commute_example
#eval pathLength farLeft
#eval generatorIndexSum yangBaxterLeft
#eval generatorIndexSum yangBaxterRight
end Examples
end Semantics.BraidedField