Thanks to Harris, Hirst, and Mossinghoff — and to the copy in the basement, which found me first.
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. Combinatorics And Graph Theory Harris Solutions Manual
While I can't reproduce a copyrighted solutions manual, I can write an original short story about such a manual, its discovery, and its curious effects. Here it is: Thanks to Harris, Hirst, and Mossinghoff — and
She stared at the page for a long time. Then she took a pencil and began to trace. Three days later, she did not go to the library. She did not go to her office. She sat in her apartment, surrounded by 47 sheets of paper, each covered with graphs. She had found the odd cycle in the diagram from page 347 — it had length 9, labeled v_1 through v_9 . And when she traced that cycle, something unlocked. At the bottom: This graph is you