simp [hc₁, hc₂, Sibling.nil]
graph✝ : Graph
a✝ : Class graph✝
path₁ path₂ : Path graph✝ a✝
h : prefix? path₁ = prefix? path₂
hp : ¬Option.isSome (prefix? path₂) = true
hc₁ : path₁ = Path.nil
hc₂ : path₂ = Path.nil
⊢ path₁ ≂ path₂
no goals