The intersection of A and B, denoted A ∩ B.
The intersection of A and B*, denoted A ∩ B. (*Just as long as A and B aren’t of the same sex.)

‘The next front in the culture war for America’s resurgent Christian fundamentalist movement may be set theory. That’s right; some fundies find the mathematical theory of sets right down there with critical thinking, mainstream paleontology and Ozzy Osbourne records:

“Unlike the “modern math” theorists, who believe that mathematics is a creation of man and thus arbitrary and relative, A Beka Book teaches that the laws of mathematics are a creation of God and thus absolute….A Beka Book provides attractive, legible, and workable traditional mathematics texts that are not burdened with modern theories such as set theory.”

Why do the fundamentalists find set theory so objectionable? It seems to be not because of what it says (unlike, say, evolutionary biology) but because of the kinds of thought it may encourage; set theory, you see, with its paradoxes and its heretical notion of there being different kinds of infinity (i.e., the set of all real numbers and the set of all integers are both infinite, but the former is greater than the latter) could subtly seduce even the most rigorously home-schooled children into modernist habits of thinking, not based in absolute truths and rigid, God-given hierarchies but in ungodly paradoxes. And if there is more than one infinity and the the set of all statements is either incomplete or inconsistent, they may start to wonder what other statements they had accepted on divinely-ordained authority are incorrect, and before you know it, you have atheism, Red Communism and buggery on the Sabbath.’ (The Null Device).