What are the ids of instructors who taught in the Fall of 2009 but not in the Spring of 2010?
return instructors ;return #1 who  taught in Falls 2009 ;return #1 who  taught in Spring 2010 ;return #1 besides  #3 ;return #1 of  both #2 and  #4 ;return ids of  #5
['select', 'filter', 'filter', 'discard', 'intersection', 'project']