@freemo don't trust a definition a mathematician invented.

My 9th grade math teacher once told us whoever got the highest grade on a test was exempt from the next class period, which was dedicated to reviewing our mistakes. Turns out there was a tie for first, so the teacher says, "Okay, Kyle AND Evan can leave," with a funny little smirk. We pack up and start walking towards the door when he tells us to stop and go sit back down. Why? Because in math "and" means the intersection, not the union. Evan and I are separate people (disjoint) so our intersection is an empty set. The teacher had really dismissed nobody at all.