exact absurd hp.symm $ ne_of_ssubset e.progress_ssubset
α : Type
inst✝ : Proper α
s s₁ s₂ : State α
hp : s₁.progress = s₂.progress
tl₁ : State α
tail₁ : Tail s₁ s₁
n : State.Nontrivial s₂
e : s₂ ↓ᵢ| s₁
a_ih✝ : State.Nontrivial s₁ → Tail s₁ s₁ → Steps s₁ s₂ → s₁.tag = s₂.tag → s₁ = s₂
ht : s₁.tag = s₂.tag
⊢ s₁ = s₂
no goals