User blog comment:Forthright/QUICK QUESTION/@comment-37224188-20191026010624/@comment-35470197-20191026142200

For a person who currently understands FGH up to 10, it is too difficult to study all ordinals below e0. Maybe the OP is not ready for the definition of the notion of a fundamental sequence, and hence w^2 is a good (non-trivial) starting point. Of course, the OP needs to understand all ordinals below e0 later.