docs: public VariableNumMap instantiateVariables(DynamicAssignment assignment) {
      List<String> varNames = Lists.newArrayList();
      List<Variable> variables = Lists.newArrayList();
      List<Integer> variableInds = Lists.newArrayList();
  
      instantiateVariablesHelper(assignment, varNames, variables, variableInds, "", 0);
      Preconditions.checkState(varNames.size() == variables.size());
      return new VariableNumMap(variableInds, varNames, variables);
    }