docs: public int[] getUniqueVariables() {
      Set<Integer> uniqueVars = Sets.newTreeSet(Ints.asList(semanticVariables));
  
      int[] uniqueVarsArray = new int[uniqueVars.size()];
      int i = 0;
      for (Integer uniqueVar : uniqueVars) {
        uniqueVarsArray[i] = uniqueVar;
        i++;
      }
  
      return uniqueVarsArray;
    }