Module: Mathlib.Algebra.Lie.Weights.IsSimple

Goal state before:
pp: case pos
K : Type u_1
L : Type u_2
inst✝⁷ : Field K
inst✝⁶ : CharZero K
inst✝⁵ : LieRing L
inst✝⁴ : LieAlgebra K L
inst✝³ : FiniteDimensional K L
inst✝² : IsKilling K L
H : LieSubalgebra K L
inst✝¹ : H.IsCartanSubalgebra
inst✝ : IsTriangularizable K (↥H) L
q : Submodule K (Dual K ↥H)
hq : ∀ (i : ↥LieSubalgebra.root), q ∈ End.invtSubmodule ↑((rootSystem H).reflection i)
χ : Weight K (↥H) L
x_χ m_α : L
hx_χ : x_χ ∈ genWeightSpace L ⇑χ
α : Weight K (↥H) L
hαq : Weight.toLinear K (↥H) L α ∈ q
hα₀ : α.IsNonZero
hm_α : m_α ∈ genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α) ⊔ corootSubmodule α
hm_α_original : m_α ∈ sl2SubmoduleOfRoot hα₀
m_αneg : L
hm_αneg : m_αneg ∈ ↑(genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α))
m_h : L
hm_h : m_h ∈ ↑(corootSubmodule α)
hm_eq : m_αneg + m_h = m_α
m_pos : L
hm_pos : m_pos ∈ ↑(genWeightSpace L ⇑α)
m_neg : L
hm_neg : m_neg ∈ ↑(genWeightSpace L (-⇑α))
hm_αneg_eq : m_pos + m_neg = m_αneg
hm_α_decomp : m_α = m_pos + m_neg + m_h
h_bracket_sum : ⁅x_χ, m_α⁆ = ⁅x_χ, m_pos⁆ + ⁅x_χ, m_neg⁆ + ⁅x_χ, m_h⁆
w_plus : Weight.toLinear K (↥H) L χ + Weight.toLinear K (↥H) L α = 0
⊢ ⁅x_χ, m_α⁆ ∈ ⨆ α, sl2SubmoduleOfRoot ⋯

pp: case neg
K : Type u_1
L : Type u_2
inst✝⁷ : Field K
inst✝⁶ : CharZero K
inst✝⁵ : LieRing L
inst✝⁴ : LieAlgebra K L
inst✝³ : FiniteDimensional K L
inst✝² : IsKilling K L
H : LieSubalgebra K L
inst✝¹ : H.IsCartanSubalgebra
inst✝ : IsTriangularizable K (↥H) L
q : Submodule K (Dual K ↥H)
hq : ∀ (i : ↥LieSubalgebra.root), q ∈ End.invtSubmodule ↑((rootSystem H).reflection i)
χ : Weight K (↥H) L
x_χ m_α : L
hx_χ : x_χ ∈ genWeightSpace L ⇑χ
α : Weight K (↥H) L
hαq : Weight.toLinear K (↥H) L α ∈ q
hα₀ : α.IsNonZero
hm_α : m_α ∈ genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α) ⊔ corootSubmodule α
hm_α_original : m_α ∈ sl2SubmoduleOfRoot hα₀
m_αneg : L
hm_αneg : m_αneg ∈ ↑(genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α))
m_h : L
hm_h : m_h ∈ ↑(corootSubmodule α)
hm_eq : m_αneg + m_h = m_α
m_pos : L
hm_pos : m_pos ∈ ↑(genWeightSpace L ⇑α)
m_neg : L
hm_neg : m_neg ∈ ↑(genWeightSpace L (-⇑α))
hm_αneg_eq : m_pos + m_neg = m_αneg
hm_α_decomp : m_α = m_pos + m_neg + m_h
h_bracket_sum : ⁅x_χ, m_α⁆ = ⁅x_χ, m_pos⁆ + ⁅x_χ, m_neg⁆ + ⁅x_χ, m_h⁆
w_plus : ¬Weight.toLinear K (↥H) L χ + Weight.toLinear K (↥H) L α = 0
⊢ ⁅x_χ, m_α⁆ ∈ ⨆ α, sl2SubmoduleOfRoot ⋯

Tactic:
· apply LieSubmodule.mem_iSup_of_mem ⟨α, hαq, hα₀⟩
    have hx_χ_in_sl2 : x_χ ∈ sl2SubalgebraOfRoot hα₀ := by
      obtain ⟨h, e, f, ht, he, hf⟩ := exists_isSl2Triple_of_weight_isNonZero hα₀
      rw [mem_sl2SubalgebraOfRoot_iff hα₀ ht he hf]
      have hx_χ_neg : x_χ ∈ genWeightSpace L (-α.toLinear) := by
        rw [← (add_eq_zero_iff_eq_neg.mp w_plus)]
        exact hx_χ
      obtain ⟨c, hc⟩ := (finrank_eq_one_iff_of_nonzero' ⟨f, hf⟩ (by simp [ht.f_ne_zero])).mp
        (finrank_rootSpace_eq_one (-α) (by simpa using hα₀)) ⟨x_χ, hx_χ_neg⟩
      exact ⟨0, c, 0, by simpa using hc.symm⟩
    apply LieSubalgebra.lie_mem <;> [exact hx_χ_in_sl2; exact hm_α_original]

Goal state after:
case neg
K : Type u_1
L : Type u_2
inst✝⁷ : Field K
inst✝⁶ : CharZero K
inst✝⁵ : LieRing L
inst✝⁴ : LieAlgebra K L
inst✝³ : FiniteDimensional K L
inst✝² : IsKilling K L
H : LieSubalgebra K L
inst✝¹ : H.IsCartanSubalgebra
inst✝ : IsTriangularizable K (↥H) L
q : Submodule K (Dual K ↥H)
hq : ∀ (i : ↥LieSubalgebra.root), q ∈ End.invtSubmodule ↑((rootSystem H).reflection i)
χ : Weight K (↥H) L
x_χ m_α : L
hx_χ : x_χ ∈ genWeightSpace L ⇑χ
α : Weight K (↥H) L
hαq : Weight.toLinear K (↥H) L α ∈ q
hα₀ : α.IsNonZero
hm_α : m_α ∈ genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α) ⊔ corootSubmodule α
hm_α_original : m_α ∈ sl2SubmoduleOfRoot hα₀
m_αneg : L
hm_αneg : m_αneg ∈ ↑(genWeightSpace L ⇑α ⊔ genWeightSpace L (-⇑α))
m_h : L
hm_h : m_h ∈ ↑(corootSubmodule α)
hm_eq : m_αneg + m_h = m_α
m_pos : L
hm_pos : m_pos ∈ ↑(genWeightSpace L ⇑α)
m_neg : L
hm_neg : m_neg ∈ ↑(genWeightSpace L (-⇑α))
hm_αneg_eq : m_pos + m_neg = m_αneg
hm_α_decomp : m_α = m_pos + m_neg + m_h
h_bracket_sum : ⁅x_χ, m_α⁆ = ⁅x_χ, m_pos⁆ + ⁅x_χ, m_neg⁆ + ⁅x_χ, m_h⁆
w_plus : ¬Weight.toLinear K (↥H) L χ + Weight.toLinear K (↥H) L α = 0
⊢ ⁅x_χ, m_α⁆ ∈ ⨆ α, sl2SubmoduleOfRoot ⋯