code: @SuppressWarnings("unchecked")
    @Override
    public Set<LeftT> alignedToRightItem(final Object rightItem) {
      if (rightToLeft.containsKey(rightItem)) {
        return rightToLeft.get((RightT)rightItem);
      } else {
        return ImmutableSet.of();
      }
    }
docs: if it's in the map, it must be RightT