from tensorflow.python.feature_column import feature_column_lib as core_feature_column

    model = estimator.GradientBoostedDecisionTreeEstimator(
        head=head_fn,
        learner_config=learner_config,
        num_trees=1,
        examples_per_layer=3,
        model_dir=model_dir,
        config=config,
        feature_columns=[core_feature_column.numeric_column("x")],
        use_core_libs=True)

    model.fit(input_fn=_train_input_fn, steps=15)
    model.evaluate(input_fn=_eval_input_fn, steps=1)
    model.export(self._export_dir_base)

