The discussion centers on the suitability of Kreyszig's and Hassani's books as prerequisites for quantum mechanics (QM). Kreyszig's book on functional analysis is highlighted as a strong resource, particularly chapters 10 and 11, which introduce essential mathematical concepts for QM. It is noted that Kreyszig's work is more rigorous and suited for those approaching QM with a mathematical mindset. In contrast, Hassani's textbook on mathematical physics is deemed sufficient for practical applications in QM and other topics, catering to those who use mathematics in a more applied manner. The conversation also clarifies that Kreyszig has authored a practical mathematics book, "Advanced Engineering Mathematics," which is more comparable to Hassani's works. Overall, both books serve different purposes depending on the reader's mathematical approach and needs in theoretical physics.