Theorem: LieAlgebra.IsKilling.root_apply_cartanEquivDual_symm_ne_zero
File: Mathlib/Algebra/Lie/Weights/Killing.lean

tactic: contrapose! hα
state_before: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α.IsNonZero
⊢ α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) ≠ 0
state_after: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
⊢ ¬α.IsNonZero

tactic: suffices (cartanEquivDual H).symm α ∈ α.ker ⊓ corootSpace α by
  rw [(disjoint_ker_weight_corootSpace α).eq_bot] at this
  simpa using this
state_before: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
⊢ ¬α.IsNonZero
state_after: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
⊢ (cartanEquivDual H).symm (Weight.toLinear K (↥H) L α) ∈
    Weight.ker ⊓ (lieIdealSubalgebra K (↥H) (corootSpace ⇑α)).toSubmodule

tactic: exact Submodule.mem_inf.mp ⟨hα, cartanEquivDual_symm_apply_mem_corootSpace K L H α⟩
state_before: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
⊢ (cartanEquivDual H).symm (Weight.toLinear K (↥H) L α) ∈
    Weight.ker ⊓ (lieIdealSubalgebra K (↥H) (corootSpace ⇑α)).toSubmodule
state_after: no goals

tactic: rw [(disjoint_ker_weight_corootSpace α).eq_bot] at this
state_before: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
this :
  (cartanEquivDual H).symm (Weight.toLinear K (↥H) L α) ∈
    Weight.ker ⊓ (lieIdealSubalgebra K (↥H) (corootSpace ⇑α)).toSubmodule
⊢ ¬α.IsNonZero
state_after: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
this : (cartanEquivDual H).symm (Weight.toLinear K (↥H) L α) ∈ ⊥
⊢ ¬α.IsNonZero

tactic: simpa using this
state_before: R : Type u_1
K : Type u_2
L : Type u_3
inst✝⁹ : CommRing R
inst✝⁸ : LieRing L
inst✝⁷ : LieAlgebra R L
inst✝⁶ : Field K
inst✝⁵ : LieAlgebra K L
inst✝⁴ : FiniteDimensional K L
H : LieSubalgebra K L
inst✝³ : H.IsCartanSubalgebra
inst✝² : IsTriangularizable K (↥H) L
inst✝¹ : IsKilling K L
inst✝ : CharZero K
α : Weight K (↥H) L
hα : α ((cartanEquivDual H).symm (Weight.toLinear K (↥H) L α)) = 0
this : (cartanEquivDual H).symm (Weight.toLinear K (↥H) L α) ∈ ⊥
⊢ ¬α.IsNonZero
state_after: no goals