Anna found the notebook in a dusty corner of the university library: a slim, coffee-stained copy of Principles of Nonlinear Optical Spectroscopy. The cover bore a name she’d only heard whispered in seminars—Mukamel—like an old wizard of light. She opened it between two classes, expecting dense equations and diagrams. Instead she found, tucked inside the front cover, a handwritten note: “If you can teach this to a friend over coffee, you understand it. —E.”