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diff --git a/src/main/java/org/apache/commons/math/distribution/ChiSquaredDistribution.java b/src/main/java/org/apache/commons/math/distribution/ChiSquaredDistribution.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.math.distribution;
+
+/**
+ * The Chi-Squared Distribution.
+ *
+ * <p>
+ * References:
+ * <ul>
+ * <li><a href="http://mathworld.wolfram.com/Chi-SquaredDistribution.html">
+ * Chi-Squared Distribution</a></li>
+ * </ul>
+ * </p>
+ *
+ * @version $Revision: 920852 $ $Date: 2010-03-09 13:53:44 +0100 (mar. 09 mars 2010) $
+ */
+public interface ChiSquaredDistribution extends ContinuousDistribution, HasDensity<Double> {
+    /**
+     * Modify the degrees of freedom.
+     * @param degreesOfFreedom the new degrees of freedom.
+     * @deprecated as of v2.1
+     */
+    @Deprecated
+    void setDegreesOfFreedom(double degreesOfFreedom);
+
+    /**
+     * Access the degrees of freedom.
+     * @return the degrees of freedom.
+     */
+    double getDegreesOfFreedom();
+
+    /**
+     * Return the probability density for a particular point.
+     * @param x  The point at which the density should be computed.
+     * @return  The pdf at point x.
+     */
+    double density(Double x);
+}