Barleywine
OK, I checked it out. Magic Without Tears, Chapter 5. He fusses around with 0^0 (0 raised to the power 0), which is undefined in mathematics. In itself, it is meaningless and cannot be defined in a consistent fashion. Ultimately, Crowley unknowingly divides by 0.
Thanks! I will have to go read that again. I seem to recall him taking it out of the realm of mathematics and into more speculative territory, but it's been a long time. I'm sure he convinced himself (of course he would), but I remember grappling with it for quite some time. If memory serves, I eventually came to terms (of some kind) with it.