Given the declarations:

x, y, z : N a : Author (i.e. a is of type set Author)

b : Books (b is of type set Books)

on_shelves : P Books ( P denotes power set)

novelists : P Author

say what the type is in each of the following terms:

a) x ___________________________

b) x + y ____________________________

c) {on_shelves} ____________________________

d) on_shelves U { b} ____________________________