You were not in the target audience. This was written for people already familiar with the theory of geometric algebras.
Like any other mathematics paper, it cannot include the content of a whole textbook inside the paper, to provide context for non-mathematicians or for mathematicians with a different specialization.
Here on HN there are every day links to "walls of text" that are trivial to understand for those familiar with computer programming, but which would be completely impossible to understand for a non-programmer.
I believe I am already familiar with the theory of geometric algebras. (Funny you mention this, since the author clearly believes that most textbook authors are not familiar with the theory of geometric algebras, and that they blindly copy each others textbooks without understanding it.)
.. how is _my_ comment flagged, when all but one other comments are just randomly jumping on the title (which has nothing to do with the article btw)? I at least claimed that I've read the first big chunk of the article (before dismissing it), while none of the other comments are about the article or show any sign that they've read the article. (And the other comment dismisses the article too, despite "being a big fan of the author".)
