Goal:
  
  G : t
  s' : VSet.t
  z : V.t
  s0 : VSet.t
  s'0 : VSet.t
  x : V.t
  y : V.t
  z0 : V.t
  d : DisjointAdd x s0 s'0
  e : EdgeOf x y
  p : SPath s0 y z0
  ss' : Disjoint s'0 s'
  q : SPath s' z0 z
  IHp : forall (ss' : Disjoint s0 s') (q : SPath s' z0 z),
        sweight (sconcat p ss' q) = sweight p + sweight q
  ============================
   (e.π1 + (sweight p + sweight q) = e.π1 + sweight p + sweight q)


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