have h : ¬(Path.cons child path₁).prefix?.isSome := by simp_all [Option.isSome_iff_exists]
graph✝ : Graph
cls✝ : Class graph✝
child : Class.Child cls✝
path₁ : Path graph✝ (Class.Child.class child)
h : prefix? (Path.cons child path₁) = none
⊢ ∃ path₂, Path.cons child path₁ ≻ path₂
graph✝ : Graph
cls✝ : Class graph✝
child : Class.Child cls✝
path₁ : Path graph✝ (Class.Child.class child)
h✝ : prefix? (Path.cons child path₁) = none
h : ¬Option.isSome (prefix? (Path.cons child path₁)) = true
⊢ ∃ path₂, Path.cons child path₁ ≻ path₂