What are the first names of all teachers who have taught a course and the corresponding course codes?
return teachers ;return courses of #1 ;return number of  #2 for each #1 ;return #1 where #3 is at least one ;return courses of #4 ;return course codes of #5 ;return first names of #4 ;return #7 ,  #6
['select', 'project', 'group', 'comparative', 'project', 'project', 'project', 'union']