let rec is_dummy_term = function
    If_const(i) ->
      (match (string_id#get_name i) with
        "dummy_agent"
      | "dummy_nat"
      | "dummy_bool"
      | "dummy_hash"
      | "dummy_msg"
      | "dummy_nonce"
      | "dummy_pk"
      | "dummy_sk"
      | "dummy_chnl"
      | "dummy_chnl_ota"
      | "dummy_chnl_dy"
      | "dummy_pid"
      | "dummy_func"
      | "dummy_set"
      | "dummy_list" -> true
      | _ -> false)
  | If_pair(t1,t2)
  | If_crypt(t1,t2)
  | If_scrypt(t1,t2) -> (is_dummy_term t1) || (is_dummy_term t2)
  | If_inv(t) -> is_dummy_term t
  | _ -> false