(* The Espec for odd is different from the Espec for even; the former has only "even" as an external function, and vice versa. *)
Existing Instance Espec.

(* Can't prove   prog_correct: semax_prog prog Vprog Gprog because there is no _main function, so prove all_funcs_correct instead. *)
Lemma all_funcs_correct:
semax_func Vprog Gprog (prog_funct prog) Gprog.