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 : VSet.elt
  p : PathOf G2 (s G2) x
  wp : 0 <= weight p
  ============================
   (∥ ∑ p : PathOf Gl (s Gl) x, ∥ 0 <= weight p ∥ ∥)


DEBUG:Going to execute:
<coq-core.plugins.ltac::constructor@0>
DEBUG LTAC Evaluated term: (source_pathOf G2 x)
DEBUG LTAC Evaluated term: (source_pathOf G2 x _view_subject_)