The paper was open in the second browser tab. I closed everything else. I worked through the abstract, then the introduction, then the formal setup, taking each definition and holding it long enough to be sure I had it before moving on. When I hit the first proof sketch I opened a scratch buffer and started rewriting the key step in my own notation. My breathing had gone even. I was inside the paper's logic now, following the argument at exactly the pace it asked for, not rushing past the steps that looked obvious and not getting stuck on the ones that looked hard. Outside this tab the world continued without me. I read on.
