case progress  =>
  have h₁ := e₁.progress_eq ▸ e₁₂.progress_eq
  have h₂ := e₂.progress_eq ▸ e₂₁.progress_eq
  rw [hr₁, hr₂] at *
  simp [h₁, h₂]
  apply Set.insert_comm
α : Type
inst✝ : Hierarchical α
s₁ s s₁₂ s₂ s₂₁ : State α
e₁ : s ↓ₛ s₁
e₁₂ : s₁ ↓ₛ s₁₂
e₂ : s ↓ₛ s₂
e₂₁ : s₂ ↓ₛ s₂₁
hr₁ : rcn e₁ = rcn e₂₁
hr₂ : rcn e₂ = rcn e₁₂
⊢ s₁₂.progress = s₂₁.progress
no goals