Goal:
  
  G : t
  s : VSet.t
  x : V.t
  p : SPath G s x x
  y : VSet.elt
  yinp : VSet.In y (snodes G p)
  rx := spath_refl G VSet.empty x : SPath G VSet.empty x x
  disj : Disjoint s VSet.empty
  c : SPath G (VSet.union s VSet.empty) y y
  wc : sweight c = sweight p + sweight rx
  ============================
   (sweight p + 0 = sweight p)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook; zify_elim_let; zify_op;
            Zify.zify_iter_specs