But below it, in a different handwriting — small, red ink — someone had written: See solution on page 347. Then see yourself.
She was not sleeping much. Chapter 11 contained the supplemental problems — ones not in the student edition. Problem 11.4 read: Let G be a graph on n vertices. Prove that either G or its complement is connected.
Elena looked up from the manual and saw the library’s reading room not as a room, but as a graph . The desks were vertices. The students were edges — no, wait: students were walks between desks. She could see the adjacency matrix of the room pulsing faintly in the air. An undergrad shuffled past, and Elena instinctively computed: degree 3, not Eulerian, but close . Combinatorics And Graph Theory Harris Solutions Manual
“Where did you learn the reflection trick ?” he asked.
The solution was not a proof. It was a single diagram: a graph with 22 vertices and 33 edges, labeled like a constellation. At the bottom: This graph is you. Trace it. Find your odd cycle. But below it, in a different handwriting —
And at the very bottom of the acknowledgments, she wrote:
She solved it in her head. Then she turned the page. Chapter 11 contained the supplemental problems — ones
Thanks to Harris, Hirst, and Mossinghoff — and to the copy in the basement, which found me first.