Lemma add_global_find_symbol: forall {F V} (g: Genv.t F V) m0 m x (G: Genv.alloc_global (Genv.add_global g x) m0 x = Some m) (N: Genv.genv_next g = Mem.nextblock m0) b (VB: Mem.valid_block m b), Mem.valid_block m0 b \/ exists id, Genv.find_symbol (Genv.add_global g x) id = Some b.