cases h
graph✝ : Graph
a✝¹ : Class graph✝
child✝ : Class.Child a✝¹
a✝ : Path graph✝ (Class.Child.class child✝)
h : Path.cons child✝ a✝ ≂ Path.nil
⊢ prefix? (Path.cons child✝ a✝) = prefix? Path.nil
case cons
graph✝ : Graph
a✝³ : Class graph✝
child✝ : Class.Child a✝³
a✝² : Path graph✝ (Class.Child.class child✝)
parent✝ : Path graph✝ a✝³
a✝¹ : Path.cons child✝ a✝² ≻ parent✝
a✝ : Path.nil ≻ parent✝
⊢ prefix? (Path.cons child✝ a✝²) = prefix? Path.nil