intro h
graph : Graph
start : Class graph
child : Class.Child start
subpath subprefix : Path graph (Class.Child.class child)
⊢ prefix? subpath = some subprefix → prefix? (cons child subpath) = some (cons child subprefix)
graph : Graph
start : Class graph
child : Class.Child start
subpath subprefix : Path graph (Class.Child.class child)
h : prefix? subpath = some subprefix
⊢ prefix? (cons child subpath) = some (cons child subprefix)