Firebird trigger before delete

I have two tables AUTHOR and BOOK connected by AUTHORID.

I need to create a trigger that in case of deleting an author, it deletes the books by that author first and after that deletes the author. And if someone just tries to update the AUTHORID field in AUTHOR it updates the AUTHORID in BOOK automatically.
Is that even doable? :)

set term # ;  
create trigger del for author  
before delete or update as  
  declare variable aut int;  
  declare variable bok int;  
begin  
  if(deleting) then  
  begin  
    delete from book where authorid=:aut;  
    delete from author where authorid=:aut;  
  end  
  if (updating) then  
  begin  
    update book set authorid=new.authorid;  
  end end#  
set term ; #