I wasn't sure whether to "announce" this formally yet -- or at all -- but what the hell. My heretofore untitled book shall henceforth be known as...
Theorems & Thaumaturgy
Advanced Arcana for the Discerning Magic-User
I like it. And I'm very pleased to have got both alliteration and an ampersand in there! What's more (according to google search) it's not a name that's been used before in any context -- which I find somewhat surprising, but ideal.
Thanks to Quibish for the oblique inspiration... I didn't end up using any of the titles or words you suggested, but somehow your ideas pushed me in a new direction where I was able to find something. (And I managed to slip the word "arcana" into the sub-title :)