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diff --git a/src/include/fst/product-weight.h b/src/include/fst/product-weight.h
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+// product-weight.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
+// Product weight set and associated semiring operation definitions.
+
+#ifndef FST_LIB_PRODUCT_WEIGHT_H__
+#define FST_LIB_PRODUCT_WEIGHT_H__
+
+#include <stack>
+#include <string>
+
+#include <fst/pair-weight.h>
+#include <fst/weight.h>
+
+
+namespace fst {
+
+// Product semiring: W1 * W2
+template<class W1, class W2>
+class ProductWeight : public PairWeight<W1, W2> {
+ public:
+  using PairWeight<W1, W2>::Zero;
+  using PairWeight<W1, W2>::One;
+  using PairWeight<W1, W2>::NoWeight;
+  using PairWeight<W1, W2>::Quantize;
+  using PairWeight<W1, W2>::Reverse;
+
+  typedef ProductWeight<typename W1::ReverseWeight, typename W2::ReverseWeight>
+  ReverseWeight;
+
+  ProductWeight() {}
+
+  ProductWeight(const PairWeight<W1, W2>& w) : PairWeight<W1, W2>(w) {}
+
+  ProductWeight(W1 w1, W2 w2) : PairWeight<W1, W2>(w1, w2) {}
+
+  static const ProductWeight<W1, W2> &Zero() {
+    static const ProductWeight<W1, W2> zero(PairWeight<W1, W2>::Zero());
+    return zero;
+  }
+
+  static const ProductWeight<W1, W2> &One() {
+    static const ProductWeight<W1, W2> one(PairWeight<W1, W2>::One());
+    return one;
+  }
+
+  static const ProductWeight<W1, W2> &NoWeight() {
+    static const ProductWeight<W1, W2> no_weight(
+        PairWeight<W1, W2>::NoWeight());
+    return no_weight;
+  }
+
+  static const string &Type() {
+    static const string type = W1::Type() + "_X_" + W2::Type();
+    return type;
+  }
+
+  static uint64 Properties() {
+    uint64 props1 = W1::Properties();
+    uint64 props2 = W2::Properties();
+    return props1 & props2 & (kLeftSemiring | kRightSemiring |
+                              kCommutative | kIdempotent);
+  }
+
+  ProductWeight<W1, W2> Quantize(float delta = kDelta) const {
+    return PairWeight<W1, W2>::Quantize(delta);
+  }
+
+  ReverseWeight Reverse() const {
+    return PairWeight<W1, W2>::Reverse();
+  }
+
+
+};
+
+template <class W1, class W2>
+inline ProductWeight<W1, W2> Plus(const ProductWeight<W1, W2> &w,
+                                  const ProductWeight<W1, W2> &v) {
+  return ProductWeight<W1, W2>(Plus(w.Value1(), v.Value1()),
+                               Plus(w.Value2(), v.Value2()));
+}
+
+template <class W1, class W2>
+inline ProductWeight<W1, W2> Times(const ProductWeight<W1, W2> &w,
+                                   const ProductWeight<W1, W2> &v) {
+  return ProductWeight<W1, W2>(Times(w.Value1(), v.Value1()),
+                               Times(w.Value2(), v.Value2()));
+}
+
+template <class W1, class W2>
+inline ProductWeight<W1, W2> Divide(const ProductWeight<W1, W2> &w,
+                                    const ProductWeight<W1, W2> &v,
+                                    DivideType typ = DIVIDE_ANY) {
+  return ProductWeight<W1, W2>(Divide(w.Value1(), v.Value1(), typ),
+                               Divide(w.Value2(), v.Value2(), typ));
+}
+
+}  // namespace fst
+
+#endif  // FST_LIB_PRODUCT_WEIGHT_H__