@BIF
  public static EAtom is_builtin(EObject m, EObject f, EObject a) {
    EAtom mod  = m.testAtom();
    EAtom fun  = f.testAtom();
    ESmall ary = a.testSmall();
    
    if (mod == null || fun == null || ary == null)
      throw ERT.badarg(m, f, a);
    
    BuiltInFunction bif = BIFUtil.getMethod(mod, fun, ary.value, false, false);