asclass ILCCompactIndex {
  S its(int idx) { ret itemToString(idx); }
  abstract S itemToString(int idx);
  abstract int numLeftPairs(int symbol);
  abstract int numRightPairs(int symbol);
  abstract int[] getLeftPairs(int symbol);
  abstract int[] getRightPairs(int symbol);
  abstract int getProdLength(int idx);
  abstract int getOccurrences(int idx);
  abstract int lookupLiteral(char c);
  int pairLeft(int idx) { ret firstIntFromLong(getPair(idx)); }
  int pairRight(int idx) { ret secondIntFromLong(getPair(idx)); }
  abstract long getPair(int idx);
  abstract int numberOfSymbols();
  abstract S filePartToString(int iFile, int from, int to);
  
  abstract IntegerIterator getRightPairsStartingWith(int symbol, S from);
  abstract IntegerIterator getLeftPairsEndingWith(int symbol, S from);
  abstract L<Int> symbolToFiles(int symbol); // values start at numberOfSymbols()
  abstract S symbolToProtocol(int symbol, O... _);
  abstract int getFile(int iFile); // iFile starts at 0
  abstract int getFileLength(int iFile); // iFile starts at 0
  abstract int nFiles();
  abstract int nLiterals();
  abstract bool isPair(int symbol);
  abstract CharacterIterator itemCharIteratorWithSkip(int symbol, int skip); 
}