simp!
case nil
V : Type u
V' : Type v
V'' : Type w
G : Digraph V
G' : Digraph V'
G'' : Digraph V''
inst✝ : DecidableEq V
v w u✝ : V
h : u✝ ∈ support nil
⊢ List.count u✝ (support (takeUntil nil u✝ h)) = 1
no goals