code: public static Operator addOperatorToRegistry(final String operatorId,
                                                   final boolean isNegated) {
          Operator op = new Operator( operatorId,
                                      isNegated );
          CACHE.put( getKey( operatorId,
                             isNegated ),
                     op );
          return op;
      }
docs: Creates a new Operator instance for the given parameters,
  adds it to the registry and return it
  
  @param operatorId the identification symbol of the operator
  @param isNegated true if it is negated
  
  @return the newly created operator