2024-11-19 09:40:08 +00:00
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/-
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Copyright (c) 2024 Joseph Tooby-Smith. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Joseph Tooby-Smith
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-/
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2025-02-03 11:54:08 +00:00
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import HepLean.Tensors.TensorSpecies.Basic
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2024-11-19 09:40:08 +00:00
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/-!
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# Pure tensors
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2024-11-19 09:44:14 +00:00
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A pure tensor is one of the form `ψ1 ⊗ ψ2 ⊗ ... ⊗ ψn`.
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We say a tensor is pure if it is of this form.
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2024-11-19 09:40:08 +00:00
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-/
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open IndexNotation
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open CategoryTheory
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open MonoidalCategory
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noncomputable section
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namespace TensorSpecies
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variable (S : TensorSpecies)
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/-- The type of tensors specified by a map to colors `c : OverColor S.C`. -/
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def Pure (c : OverColor S.C) : Type := (i : c.left) → S.FD.obj (Discrete.mk (c.hom i))
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namespace Pure
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variable {S : TensorSpecies} {c : OverColor S.C}
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/-- The group action on a pure tensor. -/
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def ρ (g : S.G) (p : Pure S c) : Pure S c := fun i ↦ (S.FD.obj (Discrete.mk (c.hom i))).ρ g (p i)
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/-- The underlying tensor of a pure tensor. -/
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def tprod (p : Pure S c) : S.F.obj c := PiTensorProduct.tprod S.k p
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/-- The map `tprod` is equivariant with respect to the group action. -/
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lemma tprod_equivariant (g : S.G) (p : Pure S c) : (ρ g p).tprod = (S.F.obj c).ρ g p.tprod := by
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2024-12-10 13:44:39 +00:00
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simp only [F_def, OverColor.lift, OverColor.lift.obj', LaxBraidedFunctor.of_toFunctor,
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OverColor.lift.objObj', Functor.id_obj, Rep.coe_of, tprod, Rep.of_ρ, MonoidHom.coe_mk,
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OneHom.coe_mk, PiTensorProduct.map_tprod]
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2024-11-19 09:40:08 +00:00
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rfl
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end Pure
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2024-11-22 15:36:34 +00:00
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/-- A tensor is pure if it is `⨂[S.k] i, p i` for some `p : Pure c`. -/
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2024-11-19 09:40:08 +00:00
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def IsPure {c : OverColor S.C} (t : S.F.obj c) : Prop := ∃ p : Pure S c, t = p.tprod
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/-- As long as we are dealing with tensors with at least one index, then the zero
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tensor is pure. -/
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lemma zero_isPure {c : OverColor S.C} [h : Nonempty c.left] : @IsPure S c 0 := by
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refine ⟨fun i => 0, ?_⟩
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simp only [Pure.tprod, Functor.id_obj]
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change 0 = PiTensorProduct.tprodCoeff S.k 1 fun i => 0
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symm
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apply PiTensorProduct.zero_tprodCoeff' (1 : S.k)
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rfl
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exact (Classical.inhabited_of_nonempty h).default
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@[simp]
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lemma Pure.tprod_isPure {c : OverColor S.C} (p : Pure S c) : S.IsPure p.tprod := ⟨p, rfl⟩
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@[simp]
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lemma action_isPure_iff_isPure {c : OverColor S.C} {ψ : S.F.obj c} (g : S.G) :
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S.IsPure ((S.F.obj c).ρ g ψ) ↔ S.IsPure ψ := by
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refine Iff.intro (fun h => ?_) (fun h => ?_)
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· obtain ⟨p, hp⟩ := h
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have hp' := congrArg ((S.F.obj c).ρ g⁻¹) hp
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simp only [Rep.ρ_inv_self_apply] at hp'
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rw [← Pure.tprod_equivariant] at hp'
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subst hp'
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exact Pure.tprod_isPure S (Pure.ρ g⁻¹ p)
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· obtain ⟨p, hp⟩ := h
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subst hp
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rw [← Pure.tprod_equivariant]
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exact Pure.tprod_isPure S (Pure.ρ g p)
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end TensorSpecies
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end
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