-- Mathlib/GroupTheory/Perm/Cycle/Factors.lean
theorem Disjoint.cycleFactorsFinset_mul_eq_union {f g : Perm α} (h : Disjoint f g) :
    cycleFactorsFinset (f * g) = cycleFactorsFinset f ∪ cycleFactorsFinset g

Proof state:
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (∀ f_1 ∈ f.cycleFactorsFinset ∪ g.cycleFactorsFinset, f_1.IsCycle) ∧
    ∃ (h : (↑(f.cycleFactorsFinset ∪ g.cycleFactorsFinset)).Pairwise Disjoint),
      (f.cycleFactorsFinset ∪ g.cycleFactorsFinset).noncommProd id ⋯ = f * g

Tactic:
refine ⟨?_, ?_, ?_⟩

Result:
case refine_1
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ ∀ f_1 ∈ f.cycleFactorsFinset ∪ g.cycleFactorsFinset, f_1.IsCycle

case refine_2
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (↑(f.cycleFactorsFinset ∪ g.cycleFactorsFinset)).Pairwise Disjoint

case refine_3
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (f.cycleFactorsFinset ∪ g.cycleFactorsFinset).noncommProd id ⋯ = f * g

Proof state:
case refine_3
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (f.cycleFactorsFinset ∪ g.cycleFactorsFinset).noncommProd id ⋯ = f * g

Tactic:
rw [noncommProd_union_of_disjoint h.disjoint_cycleFactorsFinset]

Result:
case refine_3
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ f.cycleFactorsFinset.noncommProd id ⋯ * g.cycleFactorsFinset.noncommProd id ⋯ = f * g

Proof state:
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (f * g).cycleFactorsFinset = f.cycleFactorsFinset ∪ g.cycleFactorsFinset

Tactic:
rw [cycleFactorsFinset_eq_finset]

Result:
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (∀ f_1 ∈ f.cycleFactorsFinset ∪ g.cycleFactorsFinset, f_1.IsCycle) ∧
    ∃ (h : (↑(f.cycleFactorsFinset ∪ g.cycleFactorsFinset)).Pairwise Disjoint),
      (f.cycleFactorsFinset ∪ g.cycleFactorsFinset).noncommProd id ⋯ = f * g

Proof state:
case refine_1
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ ∀ f_1 ∈ f.cycleFactorsFinset ∪ g.cycleFactorsFinset, f_1.IsCycle

Tactic:
simp [or_imp, mem_cycleFactorsFinset_iff, forall_swap]

Result:
no goals

Proof state:
case refine_2
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (↑(f.cycleFactorsFinset ∪ g.cycleFactorsFinset)).Pairwise Disjoint

Tactic:
rw [coe_union, Set.pairwise_union_of_symmetric Disjoint.symmetric]

Result:
case refine_2
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (↑f.cycleFactorsFinset).Pairwise Disjoint ∧
    (↑g.cycleFactorsFinset).Pairwise Disjoint ∧
      ∀ a ∈ ↑f.cycleFactorsFinset, ∀ b ∈ ↑g.cycleFactorsFinset, a ≠ b → a.Disjoint b

Proof state:
case refine_3
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ f.cycleFactorsFinset.noncommProd id ⋯ * g.cycleFactorsFinset.noncommProd id ⋯ = f * g

Tactic:
rw [cycleFactorsFinset_noncommProd, cycleFactorsFinset_noncommProd]

Result:
no goals

Proof state:
case refine_2
α : Type u_2
inst✝¹ : DecidableEq α
inst✝ : Fintype α
f g : Perm α
h : f.Disjoint g
⊢ (↑f.cycleFactorsFinset).Pairwise Disjoint ∧
    (↑g.cycleFactorsFinset).Pairwise Disjoint ∧
      ∀ a ∈ ↑f.cycleFactorsFinset, ∀ b ∈ ↑g.cycleFactorsFinset, a ≠ b → a.Disjoint b

Tactic:
exact
  ⟨cycleFactorsFinset_pairwise_disjoint _, cycleFactorsFinset_pairwise_disjoint _,
    fun x hx y hy _ =>
    h.mono (mem_cycleFactorsFinset_support_le hx) (mem_cycleFactorsFinset_support_le hy)⟩

Result:
no goals