ruby meta programming question

i looking during flush logging library logging.logger slight have doubt relating square code:

  logger = ::logging::logger.new(name)
  logger.add_appenders appender
  logger.additive = false

  category << logger
    def close
      @appenders.each {|a| a.close}
      h = ::logging::repository.instance.instance_variable_get :@h
      h.delete(@name)
      category << self; undef :close; end
    end
  end

i know category << logger opens adult eigen/meta/singleton category logger vigilant supplement an instance specifice tie method. however, i am accurately certain "class << self; undef :close; end" does purpose. anyone tell me means?