docs: public HeadedSyntacticCategory getCanonicalForm(Map<Integer, Integer> relabeling) {
      Preconditions.checkArgument(relabeling.size() == 0);
      int[] relabeledVariables = canonicalizeVariableArray(semanticVariables, relabeling);
      return new HeadedSyntacticCategory(syntacticCategory.getCanonicalForm(), relabeledVariables, rootIndex);
    }