-- Mathlib/GroupTheory/Perm/Finite.lean
theorem Disjoint.isConj_mul [Finite α] {σ τ π ρ : Perm α} (hc1 : IsConj σ π)
    (hc2 : IsConj τ ρ) (hd1 : Disjoint σ τ) (hd2 : Disjoint π ρ) : IsConj (σ * τ) (π * ρ)

Proof state:
case intro.intro.intro.refine_2.inr.refine_1
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxτ : τ (τ x) ≠ τ x
⊢ ¬(g * τ * g⁻¹) (g (τ x)) = g (τ x)

Tactic:
rwa [mul_apply, mul_apply, inv_apply_self, apply_eq_iff_eq]

Result:
no goals

Proof state:
case intro.intro.intro.refine_2
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx✝ : x ∈ ↑(σ * τ).support
hx : x ∈ ↑σ.support ∨ x ∈ ↑τ.support
⊢ ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨(σ * τ) x, ⋯⟩))) =
    (f * σ * f⁻¹ * (g * τ * g⁻¹))
      ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨x, ⋯⟩)))

Tactic:
rcases hx with hxσ | hxτ

Result:
case intro.intro.intro.refine_2.inl
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxσ : x ∈ ↑σ.support
⊢ ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨(σ * τ) x, ⋯⟩))) =
    (f * σ * f⁻¹ * (g * τ * g⁻¹))
      ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨x, ⋯⟩)))

case intro.intro.intro.refine_2.inr
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxτ : x ∈ ↑τ.support
⊢ ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨(σ * τ) x, ⋯⟩))) =
    (f * σ * f⁻¹ * (g * τ * g⁻¹))
      ↑((Set.union hd2'').symm (Sum.map (⇑(subtypeEquiv f ⋯)) (⇑(subtypeEquiv g ⋯)) ((Set.union hd1'') ⟨x, ⋯⟩)))

Proof state:
case intro.intro.intro.refine_2.inl.refine_2
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxσ : σ x ≠ x
h : (g * τ * g⁻¹) (f x) = f x
⊢ τ x = f⁻¹ (g (τ (g⁻¹ (f x))))

Tactic:
rw [mul_apply, mul_apply] at h

Result:
case intro.intro.intro.refine_2.inl.refine_2
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxσ : σ x ≠ x
h : g (τ (g⁻¹ (f x))) = f x
⊢ τ x = f⁻¹ (g (τ (g⁻¹ (f x))))

Proof state:
case intro.intro.intro.refine_2.inr.ha
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
hxτ : τ (τ x) ≠ τ x
⊢ ↑⟨(σ * τ) x, ⋯⟩ ∈ ↑τ.support

Tactic:
rwa [Subtype.coe_mk, Perm.mul_apply, (hd1 (τ x)).resolve_right hxτ,
  mem_coe, mem_support]

Result:
no goals

Proof state:
case intro.intro.intro.refine_2
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
⊢ ∀ (x : α) (hx : x ∈ ↑(σ * τ).support),
    ↑((((Set.ofEq hd1').trans (Set.union hd1'')).trans
            (((subtypeEquiv f ⋯).sumCongr (subtypeEquiv g ⋯)).trans ((Set.ofEq hd2').trans (Set.union hd2'')).symm))
          ⟨(σ * τ) x, ⋯⟩) =
      (f * σ * f⁻¹ * (g * τ * g⁻¹))
        ↑((((Set.ofEq hd1').trans (Set.union hd1'')).trans
              (((subtypeEquiv f ⋯).sumCongr (subtypeEquiv g ⋯)).trans ((Set.ofEq hd2').trans (Set.union hd2'')).symm))
            ⟨x, hx⟩)

Tactic:
intro x hx

Result:
case intro.intro.intro.refine_2
α : Type u
inst✝ : Finite α
σ τ : Perm α
hd1 : σ.Disjoint τ
val✝ : Fintype α
f : Perm α
hc1 : IsConj σ (f * σ * f⁻¹)
g : Perm α
hc2 : IsConj τ (g * τ * g⁻¹)
hd2 : (f * σ * f⁻¹).Disjoint (g * τ * g⁻¹)
hd1' : ↑(σ * τ).support = ↑σ.support ∪ ↑τ.support
hd2' : ↑(f * σ * f⁻¹ * (g * τ * g⁻¹)).support = ↑(f * σ * f⁻¹).support ∪ ↑(g * τ * g⁻¹).support
hd1'' : _root_.Disjoint ↑σ.support ↑τ.support
hd2'' : _root_.Disjoint ↑(f * σ * f⁻¹).support ↑(g * τ * g⁻¹).support
x : α
hx : x ∈ ↑(σ * τ).support
⊢ ↑((((Set.ofEq hd1').trans (Set.union hd1'')).trans
          (((subtypeEquiv f ⋯).sumCongr (subtypeEquiv g ⋯)).trans ((Set.ofEq hd2').trans (Set.union hd2'')).symm))
        ⟨(σ * τ) x, ⋯⟩) =
    (f * σ * f⁻¹ * (g * τ * g⁻¹))
      ↑((((Set.ofEq hd1').trans (Set.union hd1'')).trans
            (((subtypeEquiv f ⋯).sumCongr (subtypeEquiv g ⋯)).trans ((Set.ofEq hd2').trans (Set.union hd2'')).symm))
          ⟨x, hx⟩)