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diff --git a/kaldi_io/src/tools/openfst/include/fst/symbol-table-ops.h b/kaldi_io/src/tools/openfst/include/fst/symbol-table-ops.h
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+
+// 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: [email protected] (Jeffrey Sorensen)
+
+#ifndef FST_LIB_SYMBOL_TABLE_OPS_H_
+#define FST_LIB_SYMBOL_TABLE_OPS_H_
+
+#include <vector>
+using std::vector;
+#include <string>
+#include <tr1/unordered_set>
+using std::tr1::unordered_set;
+using std::tr1::unordered_multiset;
+
+
+#include <fst/fst.h>
+#include <fst/symbol-table.h>
+
+
+namespace fst {
+
+// Returns a minimal symbol table containing only symbols referenced by the
+// passed fst.  Symbols preserve their original numbering, so fst does not
+// require relabeling.
+template<class Arc>
+SymbolTable *PruneSymbolTable(const Fst<Arc> &fst, const SymbolTable &syms,
+                              bool input) {
+  unordered_set<typename Arc::Label> seen;
+  seen.insert(0);  // Always keep epslion
+  StateIterator<Fst<Arc> > siter(fst);
+  for (; !siter.Done(); siter.Next()) {
+    ArcIterator<Fst<Arc> > aiter(fst, siter.Value());
+    for (; !aiter.Done(); aiter.Next()) {
+      typename Arc::Label sym = (input) ? aiter.Value().ilabel :
+                                          aiter.Value().olabel;
+      seen.insert(sym);
+    }
+  }
+  SymbolTable *pruned = new SymbolTable(syms.Name() + "_pruned");
+  for (SymbolTableIterator stiter(syms); !stiter.Done(); stiter.Next()) {
+    typename Arc::Label label = stiter.Value();
+    if (seen.find(label) != seen.end()) {
+      pruned->AddSymbol(stiter.Symbol(), stiter.Value());
+    }
+  }
+  return pruned;
+}
+
+// Relabels a symbol table to make it a contiguous mapping.
+SymbolTable *CompactSymbolTable(const SymbolTable &syms);
+
+// Merges two SymbolTables, all symbols from left will be merged into right
+// with the same ids.  Symbols in right that have conflicting ids with those
+// in left will be assigned to value assigned from the left SymbolTable.
+// The returned symbol table will never modify symbol assignments from the left
+// side, but may do so on the right.  If right_relabel_output is non-NULL, it
+// will be assigned true if the symbols from the right table needed to be
+// reassigned.
+// A potential use case is to Compose two Fst's that have different symbol
+// tables.  You can reconcile them in the following way:
+//   Fst<Arc> a, b;
+//   bool relabel;
+//   SymbolTable *bnew = MergeSymbolTable(a.OutputSymbols(),
+//                                        b.InputSymbols(), &relabel);
+//   if (relabel) {
+//     Relabel(b, bnew, NULL);
+//   }
+//   b.SetInputSymbols(bnew);
+//   delete bnew;
+SymbolTable *MergeSymbolTable(const SymbolTable &left, const SymbolTable &right,
+                              bool *right_relabel_output = 0);
+
+// Read the symbol table from any Fst::Read()able file, without loading the
+// corresponding Fst.  Returns NULL if the Fst does not contain a symbol table
+// or the symbol table cannot be read.
+SymbolTable *FstReadSymbols(const string &filename, bool input);
+
+}  // namespace fst
+#endif  // FST_LIB_SYMBOL_TABLE_OPS_H_