2025-01-20 15:17:48 +00:00
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/-
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Copyright (c) 2025 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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import HepLean.PerturbationTheory.WickContraction.Basic
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/-!
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# Uncontracted elements
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-/
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2025-01-21 06:11:47 +00:00
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open FieldSpecification
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variable {𝓕 : FieldSpecification}
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2025-01-20 15:17:48 +00:00
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namespace WickContraction
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variable {n : ℕ} (c : WickContraction n)
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open HepLean.List
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/-- Given a Wick contraction, the finset of elements of `Fin n` which are not contracted. -/
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def uncontracted : Finset (Fin n) := Finset.filter (fun i => c.getDual? i = none) (Finset.univ)
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lemma congr_uncontracted {n m : ℕ} (c : WickContraction n) (h : n = m) :
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(c.congr h).uncontracted = Finset.map (finCongr h).toEmbedding c.uncontracted := by
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subst h
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simp
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/-- The equivalence of `Option c.uncontracted` for two propositionally equal Wick contractions. -/
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def uncontractedCongr {c c': WickContraction n} (h : c = c') :
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Option c.uncontracted ≃ Option c'.uncontracted :=
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Equiv.optionCongr (Equiv.subtypeEquivRight (by rw [h]; simp))
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@[simp]
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lemma uncontractedCongr_none {c c': WickContraction n} (h : c = c') :
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(uncontractedCongr h) none = none := by
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simp [uncontractedCongr]
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@[simp]
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lemma uncontractedCongr_some {c c': WickContraction n} (h : c = c') (i : c.uncontracted) :
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(uncontractedCongr h) (some i) = some (Equiv.subtypeEquivRight (by rw [h]; simp) i) := by
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simp [uncontractedCongr]
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lemma mem_uncontracted_iff_not_contracted (i : Fin n) :
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i ∈ c.uncontracted ↔ ∀ p ∈ c.1, i ∉ p := by
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simp only [uncontracted, getDual?, Finset.mem_filter, Finset.mem_univ, true_and]
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apply Iff.intro
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· intro h p hp
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have hp := c.2.1 p hp
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rw [Finset.card_eq_two] at hp
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obtain ⟨a, b, ha, hb, hab⟩ := hp
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rw [Fin.find_eq_none_iff] at h
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by_contra hn
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simp only [Finset.mem_insert, Finset.mem_singleton] at hn
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rcases hn with hn | hn
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· subst hn
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exact h b hp
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· subst hn
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rw [Finset.pair_comm] at hp
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exact h a hp
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· intro h
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rw [Fin.find_eq_none_iff]
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by_contra hn
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simp only [not_forall, Decidable.not_not] at hn
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obtain ⟨j, hj⟩ := hn
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apply h {i, j} hj
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simp
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end WickContraction
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