simp only [← add_assoc, add_tsub_cancel_right]
V : Type u
V' : Type v
V'' : Type w
G : Digraph V
G' : Digraph V'
G'' : Digraph V''
inst✝ : DecidableEq V
u v w : V
p : Walk G u v
p' : Walk G v w
⊢ {u} + ↑(List.tail (support p)) + ↑(List.tail (support p')) =
    {u} + ↑(List.tail (support p)) + (↑(List.tail (support p')) + {v}) - {v}
no goals