Goal:
  
  G : t
  l : labelling
  Gl := relabel G l : t
  sG0 : l (s G) = 0%nat
  sG : VSet.In (s G) (V G)
  wG : forall x : VSet.elt,
       VSet.In x (V G) -> ∥ ∑ p : PathOf G (s G) x, ∥ 0 <= weight p ∥ ∥
  e : EdgeSet.elt
  e' : Edge.t
  _b_ : EdgeSet.In e' (E G)
  ============================
   (EdgeSet.In e' (E G))


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 ])