[alpinisme]

While there may be genuine issues with the book, especially when used as a first text, this strikes me as evidence either that the book was only taught through a few chapters or that the students simply didn't understand anything from it (which may be the fault of the book, of course -- but it also may be the fault of the instructor, or the preparedness of the students for the course).

Chapters 5-8 are all on operators (i.e., the entire second half of the book!). One of the most common exercises in the book is "give an example of..." And chapters 7 and 8 are literally titled "Operators on Inner Product Spaces" and "Operators on Complex Vector Spaces." If you can complete the homework with a passing grade and then pass an exam covering that material, there's no way you don't know examples of operators. Possibly you forgot the definition, but a quick, one-sentence reminder of that should make it easy to list plenty of examples)