def limit_results(partial_results, limiter_method, cumulator_method)
      return [] if partial_results.empty? # guard clause
      results_allowed = results_allowed_from(partial_results, limiter_method)
      cumulate_total(results_allowed.length, cumulator_method)
      results_allowed
    end
def limit_results(partial_results, limiter_method, cumulator_method)
      return [] if partial_results.empty? # guard clause
      results_allowed = results_allowed_from(partial_results, limiter_method)
      cumulate_total(results_allowed.length, cumulator_method)
      results_allowed
    end
limiter_method and cumulator_method must be inverses
 i.e. :- and :+, or :/ and :*