On paper, it’s one of the simplest math problems in the world: 2+2. If you’re counting something, like screws at the hardware store, it’s pretty straightforward. But the lines blur in other contexts.

A simple 2+2 problem became a paradox when real-world context intervened, sparking Kareem Carr’s debate on definitions and axioms. Carr and others show how context bent arithmetic, such as angles ...