intro h
case mpr
graph : Graph
start : Class graph
child : Class.Child start
path₁ path₂ : Path graph (Class.Child.class child)
⊢ prefix? (cons child path₁) = some (cons child path₂) → prefix? path₁ = some path₂
case mpr
graph : Graph
start : Class graph
child : Class.Child start
path₁ path₂ : Path graph (Class.Child.class child)
h : prefix? (cons child path₁) = some (cons child path₂)
⊢ prefix? path₁ = some path₂