"It's never just variables. And variables are never just numbers on a page."
The grudging student sat on the floor, books spread in a circle around him.
"The number of noses on the human face is a variable. The number of hearts that beat in their chests; personalities, souls. Infinite universes; infinite possibilities; infinite variables. Switch them." The tutor nudged one book [bound in red leather] with his foot. "Any two. You might get something interesting, you might get something trivial." He shrugged. "You might get something wrong."

The boy hugged the red-eared puppy in his lap. "I'm a bit young to get multiverses wrong," he said wearily. "I'm only twelve."
"Age is relative."
"Relativity is nonsense. And so is math."
"No, no. It's good fun. Look, doesn't the idea of giving me multiple noses intrigue you even slightly?"
"Your chins multiply," the boy sulked, "I don't see why your nose can't do the same."