# File lib/rubygems/commands/update_command.rb, line 87
      def which_to_update(highest_installed_gems, remote_gemspecs)
        result = []
        highest_installed_gems.each do |l_name, l_spec|
          highest_remote_gem =
            remote_gemspecs.select  { |spec| spec.name == l_name }.
                            sort_by { |spec| spec.version }.
                            last
          if highest_remote_gem and l_spec.version < highest_remote_gem.version
            result << l_name
          end
        end
        result
      end