(* fetching rhs functions names *)
Definition rhs_funcs ru :=  (* => Syntax.v ? *)
  match ru with
  | rule_intro _ _ t => functions_of_term t
  end.Definition all_rhs_funcs prg := flat_map rhs_funcs prg.

Lemma get_rank_eq f trs inf: assoc Nat.eqb f (infos trs) = Some inf → rank inf = get_rank trs f.