Goal:
  
  G : t
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x s0 s'
  e : EdgeOf x y
  p : SPath s0 y z
  IHp : forall (s' : VSet.t) (Hs : VSet.Subset s0 s'),
        sweight (SPath_sub Hs p) = sweight p
  s'0 : VSet.t
  Hs : VSet.Subset s' s'0
  ============================
   (e.π1 + sweight p = e.π1 + sweight p)


DEBUG:Going to execute:
let rec do_ccl :=
            try do_atom; repeat (do_intro; try do_atom); try arith_congr;
             (solve [ split; do_ccl ])
           in
           (solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"