User blog comment:Googleaarex/My number is bigger! (Googology Wiki version)/@comment-2033667-20140919220815/@comment-5029411-20140921000212

in fourth-order set theory, we have the x, xx, and xxx variables, plus xxxx' xxxx'' xxxx xxxx' etc. the xxx variables are collections of collections of classes.

in fourth-order set theory, we have the x, xx, xxx, and xxxx variables, plus xxxxx' xxxxx'' xxxxx xxxxx' etc. the xxx variables are collections of collections of collections of classes.