PhysLean/HepLean/AnomalyCancellation/PureU1/VectorLike.lean

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/-
Copyright (c) 2024 Joseph Tooby-Smith. All rights reserved.
Released under Apache 2.0 license.
Authors: Joseph Tooby-Smith
-/
import HepLean.AnomalyCancellation.PureU1.Sort
import Mathlib.Logic.Equiv.Fin
/-!
# Vector like charges
For the `n`-even case we define the property of a charge assignment being vector like.
## TODO
The `n`-odd case.
-/
universe v u
open Nat
open Finset
open BigOperators
namespace PureU1
variable {n : }
/--
Given a natural number `n`, this lemma proves that `n + n` is equal to `2 * n`.
-/
lemma split_equal (n : ) : n + n = 2 * n := (Nat.two_mul n).symm
lemma split_odd (n : ) : n + 1 + n = 2 * n + 1 := by omega
/-- A charge configuration for n even is vector like if when sorted the `i`th element
is equal to the negative of the `n + i`th element. -/
@[simp]
def VectorLikeEven (S : (PureU1 (2 * n)).Charges) : Prop :=
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∀ (i : Fin n), (sort S) (Fin.cast (split_equal n) (Fin.castAdd n i))
= - (sort S) (Fin.cast (split_equal n) (Fin.natAdd n i))
end PureU1