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diff --git a/guava/src/com/google/common/collect/BstPath.java b/guava/src/com/google/common/collect/BstPath.java
new file mode 100644
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+++ b/guava/src/com/google/common/collect/BstPath.java
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+/*
+ * Copyright (C) 2011 The Guava Authors
+ *
+ * Licensed 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 com.google.common.collect;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.annotations.GwtCompatible;
+
+import javax.annotation.Nullable;
+
+/**
+ * A path to a node in a binary search tree, originating at the root.
+ *
+ * @author Louis Wasserman
+ * @param <N> The type of nodes in this binary search tree.
+ * @param <P> This path type, and the path type of all suffix paths.
+ */
+@GwtCompatible
+abstract class BstPath<N extends BstNode<?, N>, P extends BstPath<N, P>> {
+  private final N tip;
+  @Nullable
+  private final P prefix;
+
+  BstPath(N tip, @Nullable P prefix) {
+    this.tip = checkNotNull(tip);
+    this.prefix = prefix;
+  }
+
+  /**
+   * Return the end of this {@code BstPath}, the deepest node in the path.
+   */
+  public final N getTip() {
+    return tip;
+  }
+
+  /**
+   * Returns {@code true} if this path has a prefix.
+   */
+  public final boolean hasPrefix() {
+    return prefix != null;
+  }
+
+  /**
+   * Returns the prefix of this path, which reaches to the parent of the end of this path. Returns
+   * {@code null} if this path has no prefix.
+   */
+  @Nullable
+  public final P prefixOrNull() {
+    return prefix;
+  }
+
+  /**
+   * Returns the prefix of this path, which reaches to the parent of the end of this path.
+   *
+   * @throws IllegalStateException if this path has no prefix.
+   */
+  public final P getPrefix() {
+    checkState(hasPrefix());
+    return prefix;
+  }
+}