PhysLean/HepLean/Tensors/TensorSpecies/RepIso.lean

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/-
Copyright (c) 2024 Joseph Tooby-Smith. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Tooby-Smith
-/
import HepLean.Tensors.TensorSpecies.Basic
/-!
# Isomorphism between rep of color `c` and rep of dual color.
-/
open IndexNotation
open CategoryTheory
open MonoidalCategory
noncomputable section
namespace TensorSpecies
variable (S : TensorSpecies)
/-- The morphism from `S.FD.obj (Discrete.mk c)` to `S.FD.obj (Discrete.mk (S.τ c))`
defined by contracting with the metric. -/
def toDualRep (c : S.C) : S.FD.obj (Discrete.mk c) ⟶ S.FD.obj (Discrete.mk (S.τ c)) :=
(ρ_ (S.FD.obj (Discrete.mk c))).inv
≫ (S.FD.obj { as := c } ◁ (S.metric.app (Discrete.mk (S.τ c))))
≫ (α_ (S.FD.obj (Discrete.mk c)) (S.FD.obj (Discrete.mk (S.τ c)))
(S.FD.obj (Discrete.mk (S.τ c)))).inv
≫ (S.contr.app (Discrete.mk c) ▷ S.FD.obj { as := S.τ c })
≫ (λ_ (S.FD.obj (Discrete.mk (S.τ c)))).hom
/-- The `toDualRep` for equal colors is the same, up-to conjugation by a trivial equivalence. -/
lemma toDualRep_congr {c c' : S.C} (h : c = c') : S.toDualRep c = S.FD.map (Discrete.eqToHom h) ≫
S.toDualRep c' ≫ S.FD.map (Discrete.eqToHom (congrArg S.τ h.symm)) := by
subst h
simp only [eqToHom_refl, Discrete.functor_map_id, Category.comp_id, Category.id_comp]
/-- The morphism from `S.FD.obj (Discrete.mk (S.τ c))` to `S.FD.obj (Discrete.mk c)`
defined by contracting with the metric. -/
def fromDualRep (c : S.C) : S.FD.obj (Discrete.mk (S.τ c)) ⟶ S.FD.obj (Discrete.mk c) :=
S.toDualRep (S.τ c) ≫ S.FD.map (Discrete.eqToHom (S.τ_involution c))
end TensorSpecies
end