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); 

}