static public int mergeDiskHyperGraphs(int ngramStateID, boolean saveModelCosts, int totalNumSent,
boolean useUniqueNbest, boolean useTreeNbest,
String filePrefix1, String filePrefix2, String filePrefixOut, boolean removeDuplicate) throws IOException{
SymbolTable symbolTbl = new BuildinSymbol();
DiskHyperGraph diskHG1 = new DiskHyperGraph(symbolTbl, ngramStateID, saveModelCosts, null);
diskHG1.initRead(filePrefix1+".hg.items", filePrefix1+".hg.rules", null);
DiskHyperGraph diskHG2 = new DiskHyperGraph(symbolTbl, ngramStateID, saveModelCosts, null);