User blog comment:Deedlit11/Is BEAF well-defined?/@comment-25418284-20121121205547/@comment-25418284-20121123221116

We can all agree that a structure is essentially an ordinal. For example, epsilon-0 is a tetrational space. (We'll also say that compound structures like X + 1 or X^X + X are legitimate.) Knowing this, how can we define the terms "previous structure" and "prime block"?