case mp.cons => simp [prefix?, h]; rfl
graph : Graph
start : Class graph
child : Class.Child start
path₂ : Path graph (Class.Child.class child)
child✝ : Class.Child (Class.Child.class child)
a✝ : Path graph (Class.Child.class child✝)
h : prefix? (cons child✝ a✝) = some path₂
⊢ prefix? (cons child (cons child✝ a✝)) = some (cons child path₂)
no goals