Find the first name of the professor who is teaching two courses with code CIS-220 and QM-261.
return professors ;return courses of #1 ;return code of #2 ;return #1 where #3 is CIS-220 ;return #1 where #3 is QM-261 ;return #1 in  both #4 and  #5 ;return first name of #6
['select', 'project', 'project', 'comparative', 'comparative', 'intersection', 'project']