simp at hc₁
graph✝ : Graph
a✝ : Class graph✝
path₁ path₂ : Path graph✝ a✝
h : prefix? path₁ = prefix? path₂
hp : ¬Option.isSome (prefix? path₁) = true
hc₁ : isNil path₁ = true
⊢ path₁ ≂ path₂
graph✝ : Graph
a✝ : Class graph✝
path₁ path₂ : Path graph✝ a✝
h : prefix? path₁ = prefix? path₂
hp : ¬Option.isSome (prefix? path₁) = true
hc₁ : path₁ = Path.nil
⊢ path₁ ≂ path₂