Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 18921)
+++ wp-includes/taxonomy.php	(working copy)
@@ -3138,6 +3138,17 @@
 }
 
 /**
+ * Determine if the child is on the inheritence chain fom the given parent
+ * @param int $parent the ID of the parent object
+ * @param int $child the ID of the child object
+ * @param string $object_type the relationship type (e.g. 'category')
+ * @return bool
+ */
+function has_child_relationship( $parent, $child, $object_type ) {
+	return in_array( $parent, get_ancestors( $child, $object_type ) );
+}
+
+/**
  * Returns the term's parent's term_ID
  *
  * @since 3.1.0