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diff --git a/libdimension/prtree.h b/libdimension/prtree.h
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+/*************************************************************************
+ * Copyright (C) 2010 Tavian Barnes <tavianator@gmail.com>               *
+ *                                                                       *
+ * This file is part of The Dimension Library.                           *
+ *                                                                       *
+ * The Dimension Library is free software; you can redistribute it and/  *
+ * or modify it under the terms of the GNU Lesser General Public License *
+ * as published by the Free Software Foundation; either version 3 of the *
+ * License, or (at your option) any later version.                       *
+ *                                                                       *
+ * The Dimension Library is distributed in the hope that it will be      *
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty   *
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
+ * Lesser General Public License for more details.                       *
+ *                                                                       *
+ * You should have received a copy of the GNU Lesser General Public      *
+ * License along with this program.  If not, see                         *
+ * <http://www.gnu.org/licenses/>.                                       *
+ *************************************************************************/
+
+/*
+ * Priority R-Trees for storing bounding box hierarchies.  PR-trees are a data
+ * structure introduced by Arge, de Berg, Haverkort, and Yi, which provides
+ * asymptotically optimal worst-case lookup, while remaining efficient with real-world
+ * data.  Their structure is derived from B-trees.
+ */
+
+#ifndef DIMENSION_IMPL_PRTREE_H
+#define DIMENSION_IMPL_PRTREE_H
+
+#include <stdbool.h>
+
+/* Number of children per node */
+#define DMNSN_PRTREE_B 6
+
+typedef struct dmnsn_prtree {
+  /* Children (objects or subtrees) */
+  void *children[DMNSN_PRTREE_B];
+  bool is_leaf;
+
+  /* Bounding box */
+  dmnsn_bounding_box bounding_box;
+} dmnsn_prtree;
+
+dmnsn_prtree *dmnsn_new_prtree(const dmnsn_array *objects);
+void dmnsn_delete_prtree(dmnsn_prtree *tree);
+
+bool dmnsn_prtree_search(const dmnsn_prtree *tree, dmnsn_line ray,
+                         dmnsn_intersection *intersection);
+
+#endif /* DIMENSION_IMPL_PRTREE_H */