Goal:
    G1 : t  ext : EdgeSet.t  v : VSet.elt  s : VSet.t  H1 : VSet.In v (V G1)
  ============================
   (VSet.In v (V G1))


DEBUG:Going to execute:
trivial; hnf; intros; (solve
            [ do
            ![ solve
             [ trivial | apply : eq_sym ; trivial ]
             | discriminate
             | contradiction
             | Ltac.split ]
            | case not_locked_false_eq_true; Ltac.assumption
            | match goal with
              | H:~ _ |- _ => solve [ case H; trivial ]
              end ])