def METHOD_NAME(X_1, X_2, y_1, y_2):
    estimator1.fit(X_1, y_1)
    estimator2.fit(X_1, y_1)
    est1_score = scorer(estimator1, X_2, y_2)
    est2_score = scorer(estimator2, X_2, y_2)
    METHOD_NAME = est1_score - est2_score
    return METHOD_NAME