+        assert not other.chunk_set.exists()
+        other.delete()
+
+    @transaction.commit_on_success
+    def prepend_history(self, other):
+        """Prepend history from all the other book's chunks to own."""
+        assert self != other
+
+        for i in range(len(self), len(other)):
+            title = u"pusta część %d" % i
+            chunk = self.add(slughifi(title), title)
+            chunk.commit('')
+
+        for i in range(len(other)):
+            self[i].prepend_history(other[0])
+
+        assert not other.chunk_set.exists()