bool LetterNodeListMap::HasLetter( char letter ) {
  int letter_index = IndexForChar( letter );
  std::list< LetterNode * > *list = letters_[ letter_index ];
  return list;
}
std::list< LetterNode * > *LetterNodeListMap::ListPointerAt( char letter ) {
  return letters_[ IndexForChar( letter ) ];
}
bool LetterNodeListMap::HasLetter( char letter ) const {
  return letters_[ IndexForChar( letter ) ] != NULL;
}