"Meet me at the library at 7 PM. I need your help with a mystery."

It turned out that Jack had been creating his own problem sets using Govorov's book and was using the missing solutions as a way to challenge his classmates. He had been secretly modifying the PDF file and sharing it online, where it had been downloaded by other students.

Alex's curiosity was piqued. He arrived at the library, and Rachel was already seated at a table, surrounded by stacks of math textbooks and papers. She handed him a worn-out copy of "Problems in Mathematics" by V. Govorov.

From that day on, Alex, Rachel, and Jack formed an unofficial study group, tackling tough math problems and exploring the depths of "Problems in Mathematics" by V. Govorov.