Richard Rahl, the protagonist of the bestselling Sword of Truth series, seeks to protect the world from an evil spell which (among other things) has removed his wife from existence.
As Kati Voigt points out to me, in the fifth chapter of this tenth novel in the series, Richard makes use of a relationship between math and magic to explain his reasoning to some of his partners. For example:
(quoted from Phantom)
Ann's face had gone crimson. "It's a spellform! It's inert! It can't be biological!"
"That's the problem," Richard said, answering her point rather than her anger. "You can't have these kind of variables tainting what's supposed to be a constant. It would be like a math equation in which any of the numbers could spontaneously change their value. Such a thing would render math invalid and unworkable. Algebraic symbols can vary  but even then they are specific relational variables. The numbers, though, are constants. Same with this structure: emblems have to be constructed of inert constants  you might say like simple addition or subtractions. An interval variable currupts the constant of an emblematic form."
"I don't follow," Zedd admitted.
Richard gestured to the table. "You drew the Grace in blood. The Grace is a constant. The blood is biological. Why did you do it that way?"
"To make it work," Ann snapped. "We had to do it that way in order to initiate an interior perspective of the verification web. That's the way it's done. That's the method."
Richard held up a finder. "Exactly. You deliberately introduced a controlled biological variable  blood  into what is a constant  a Grace. Keep in mind though, that it remains outside the spellform itself; it's merely an empowering agent, a catalyst. I think it must be that such a variable in the Grace allows the spell you nitiated to run its course without being influenced by a constant  the Grace. Do you see? ..."

I don't really see what he is getting at, even though I work with variables and constants for a living. And, it appears that there is only this one chapter of the book (which is only one in a series) that discusses math so explicitly. So, you might say that this tiny amount of mathematical nonsense is not worth including on this database. However, I find it terribly interesting the way Richard seems to be able to use math to understand the magic whereas his colleagues just have memorized some techniques that work. This seems very much like a role that mathematics plays in the real world as well.
Moreover, this is only one of a large number of works of fiction which draw analogies between math and magic. (See the list of "similar" works below.) This, I think, is "emblematic" (to use one of Richard Rahl's favorite terms) of the fact that many people find mathematics to be incomprehensible and powerful, like magical spells.
Thanks to Kati Voigt for pointing out this small but interesting bit of mathematical fiction!
