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diff --git a/src/include/fst/extensions/pdt/reverse.h b/src/include/fst/extensions/pdt/reverse.h
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+++ b/src/include/fst/extensions/pdt/reverse.h
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+// reverse.h
+
+// 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.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: riley@google.com (Michael Riley)
+//
+// \file
+// Expand a PDT to an FST.
+
+#ifndef FST_EXTENSIONS_PDT_REVERSE_H__
+#define FST_EXTENSIONS_PDT_REVERSE_H__
+
+#include <unordered_map>
+using std::tr1::unordered_map;
+using std::tr1::unordered_multimap;
+#include <vector>
+using std::vector;
+
+#include <fst/mutable-fst.h>
+#include <fst/relabel.h>
+#include <fst/reverse.h>
+
+namespace fst {
+
+// Reverses a pushdown transducer (PDT) encoded as an FST.
+template<class Arc, class RevArc>
+void Reverse(const Fst<Arc> &ifst,
+             const vector<pair<typename Arc::Label,
+             typename Arc::Label> > &parens,
+             MutableFst<RevArc> *ofst) {
+  typedef typename Arc::Label Label;
+
+  // Reverses FST
+  Reverse(ifst, ofst);
+
+  // Exchanges open and close parenthesis pairs
+  vector<pair<Label, Label> > relabel_pairs;
+  for (size_t i = 0; i < parens.size(); ++i) {
+    relabel_pairs.push_back(make_pair(parens[i].first, parens[i].second));
+    relabel_pairs.push_back(make_pair(parens[i].second, parens[i].first));
+  }
+  Relabel(ofst, relabel_pairs, relabel_pairs);
+}
+
+}  // namespace fst
+
+#endif  // FST_EXTENSIONS_PDT_REVERSE_H__