Instance EqDec_Z : EqDec Z := zeq.

Lemma find_symbol_globalenv {F}:
forall (prog: program F) i b,
list_norepet (prog_defs_names prog) ->
Genv.find_symbol (Genv.globalenv prog) i = Some b ->
0 < Z.pos b <= Z_of_nat (length (prog_defs prog)) /\
exists d, nth_error (prog_defs prog) (nat_of_Z (Z.pos b-1)) = Some (i,d).