contradiction
graph✝ : Graph
a✝² : Class graph✝
child✝ : Class.Child a✝²
a✝¹ : Path graph✝ (Class.Child.class child✝)
parent✝ : Path graph✝ a✝²
a✝ : Path.cons child✝ a✝¹ ≻ parent✝
h : Path.nil ≻ parent✝
this : isCons Path.nil = true
⊢ prefix? (Path.cons child✝ a✝¹) = prefix? Path.nil
no goals