$$ Function f: Define a function f that maps each book to one or more categories. Discuss how this function ensures that each book is categorized appropriately.

Function f: B $->$ P$($C$)$ this function maps out each book to one or more categories since P$($C$)$ is the power set of C$,$ meaning that each book can belong to one or more categories

d$)$ Evaluate if f is a well$-$defined function. If a book can belong to multiple categories, how does this affect the function's definition? Are there any cases where a book might not fit into any category?