author$($author$,$ id$,$ first$\_$name, last,name$)$

author pub$($author$,$ id$,$ pub$\_$id$,$ author position$)$

book$($book$-$aid, book$-$title, month, year, editor$)$

pub$($pub$\_$id$,$ title, book$\_$jid$)$

author $\_$id in author pub is a foreign lary referencing author

pubjid in author pub is a foreign loey referencing pub

booktid in pub is a foreign loey referencing book:

editor in book is a foreign bry referencing author$($awthor$\_$id$)$

Primary brys are urslerlined

Pubs Database State

What question does the following expression answer?

$|{}_{autho{r}_{i}d}($ author $)-{}_{\text{e}\text{d}\text{i}\text{t}\text{o}\text{r}}($ book $)|$

a$.$ The number of authors that have both authored and edited books.

b$.$ How many authors are not book editors.

c$.$ The total number of authors and editors across all books.

d$.$ Returns the names of all authors who have at least one publication in the database.