@@ -98,6 +98,7 @@ variable [FiniteDimensional K L] (H : LieSubalgebra K L) [H.IsCartanSubalgebra]
9898section
9999variable [IsTriangularizable K H L]
100100
101+ set_option backward.isDefEq.respectTransparency false in
101102/-- For any `α` and `β`, the corresponding root spaces are orthogonal with respect to the Killing
102103form, provided `α + β ≠ 0`. -/
103104lemma killingForm_apply_eq_zero_of_mem_rootSpace_of_add_ne_zero {α β : H → K} {x y : L}
@@ -540,6 +541,7 @@ lemma traceForm_eq_zero_of_mem_ker_of_mem_span_coroot {α : Weight K H L} {x y :
540541 root_apply_coroot hβ]
541542 · simp [root_apply_coroot hα]
542543
544+ set_option backward.isDefEq.respectTransparency false in
543545lemma exists_isSl2Triple_of_weight_isNonZero {α : Weight K H L} (hα : α.IsNonZero) :
544546 ∃ h e f : L, IsSl2Triple h e f ∧ e ∈ rootSpace H α ∧ f ∈ rootSpace H (-α) := by
545547 obtain ⟨e, heα : e ∈ rootSpace H α, he₀ : e ≠ 0 ⟩ := α.exists_ne_zero
@@ -568,6 +570,7 @@ lemma exists_isSl2Triple_of_weight_isNonZero {α : Weight K H L} (hα : α.IsNon
568570 rw [lie_smul, lie_smul, smul_lie, this]
569571 simp [← smul_assoc, f, hh, mul_comm _ (2 * (α h)⁻¹)]
570572
573+ set_option backward.isDefEq.respectTransparency false in
571574lemma _root_.IsSl2Triple.h_eq_coroot {α : Weight K H L} (hα : α.IsNonZero)
572575 {h e f : L} (ht : IsSl2Triple h e f) (heα : e ∈ rootSpace H α) (hfα : f ∈ rootSpace H (-α)) :
573576 h = coroot α := by
@@ -623,6 +626,7 @@ noncomputable def sl2SubalgebraOfRoot {α : Weight K H L} (hα : α.IsNonZero) :
623626 choose h e f t ht using exists_isSl2Triple_of_weight_isNonZero hα
624627 exact t.toLieSubalgebra K
625628
629+ set_option backward.isDefEq.respectTransparency false in
626630lemma mem_sl2SubalgebraOfRoot_iff {α : Weight K H L} (hα : α.IsNonZero) {h e f : L}
627631 (t : IsSl2Triple h e f) (hte : e ∈ rootSpace H α) (htf : f ∈ rootSpace H (-α)) {x : L} :
628632 x ∈ sl2SubalgebraOfRoot hα ↔ ∃ c₁ c₂ c₃ : K, x = c₁ • e + c₂ • f + c₃ • ⁅e, f⁆ := by
@@ -675,6 +679,7 @@ This represents the image of the coroot space under the inclusion `H ↪ L`. -/
675679noncomputable abbrev corootSubmodule (α : Weight K H L) : LieSubmodule K H L :=
676680 LieSubmodule.map H.toLieSubmodule.incl (corootSpace α)
677681
682+ set_option backward.isDefEq.respectTransparency false in
678683open Submodule in
679684lemma sl2SubmoduleOfRoot_eq_sup (α : Weight K H L) (hα : α.IsNonZero) :
680685 sl2SubmoduleOfRoot hα = genWeightSpace L α ⊔ genWeightSpace L (-α) ⊔ corootSubmodule α := by
@@ -715,6 +720,7 @@ lemma sl2SubmoduleOfRoot_ne_bot (α : Weight K H L) (hα : α.IsNonZero) :
715720/-- The collection of roots as a `Finset`. -/
716721noncomputable abbrev _root_.LieSubalgebra.root : Finset (Weight K H L) := {α | α.IsNonZero}
717722
723+ set_option backward.isDefEq.respectTransparency false in
718724lemma restrict_killingForm_eq_sum :
719725 (killingForm K L).restrict H = ∑ α ∈ H.root, (α : H →ₗ[K] K).smulRight (α : H →ₗ[K] K) := by
720726 rw [restrict_killingForm, traceForm_eq_sum_finrank_nsmul' K H L]
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