Leo sat back. He could almost hear Roger Bowley’s voice—kind but firm, from decades past. The solution manual wasn’t a shortcut. It was a map, yes, but it also guarded one small wilderness where he had to find his own way.

He closed the PDF, picked up his pencil, and for the first time all night, began to truly think.

And in the silence of 3 AM, Leo finally understood why Bowley had left that one problem blank.