case cons child₁ subpath₁ hi =>
  cases subpath₁
  case nil => rfl
  case cons child₂ subpath₂ => simp [isCons]
graph : Graph
start start✝ : Class graph
child₁ : Class.Child start✝
subpath₁ : Path graph (Class.Child.class child₁)
hi : Option.isSome (prefix? subpath₁) = true → isCons subpath₁ = true
h : Option.isSome (prefix? (cons child₁ subpath₁)) = true
⊢ isCons (cons child₁ subpath₁) = true
no goals