Goal:
  
  G1 : t
  G2 : t
  l : labelling
  Gl := relabel_on G1 G2 l : t
  H : invariants G1
  preserves_edges : forall e : EdgeSet.elt,
                    EdgeSet.In e (E G1) -> EdgeSet.In e (E G2)
  HGl : correct_labelling G1 l
  H0 : invariants G2
  H1 : acyclic_no_loop G2
  embed : forall v1 v2 : VSet.elt,
          VSet.In v1 (V G1) ->
          VSet.In v2 (V G1) -> (lsp G2 v1 v2 <= lsp G1 v1 v2)%nbar
  x : V.t
  s : VSet.t
  p : SPath Gl s x x
  ============================
   ((Some (sweight p) <= lsp G2 x x)%nbar -> sweight p > 0 -> False)


DEBUG:Going to execute:
rewrite lsp_xx /=
DEBUG LTAC Evaluated term: wp
DEBUG LTAC Evaluated term: E
DEBUG LTAC Evaluated term: VSet.choose_spec2
DEBUG LTAC Evaluated term: (VSet.choose_spec2 _view_subject_)
DEBUG LTAC Evaluated term: (sweight_relabel_on_G2 p)
DEBUG LTAC Evaluated term: (sweight_relabel_on_G2 p
                              (VSet.choose_spec2 _view_subject_))