Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : ~ VSet.In y (V G)
  Hle : leq_vertices G n x y
  nneg : n <= 0
  n0 : x <> y
  Vx : VSet.In x (V G)
  e : x = s G
  Hxs : lsp0 G (V G) (s G) (s G) = None
  H : (Some (sweight (spath_refl G (V G) (s G))) <= None)%nbar
  ============================
   (x <> s G)


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"