Find all airlines that have flights from airport 'CVO' but not from 'APG'.
return airlines ;return flights of #1 ;return airports of #2 ;return #1 where #3 is  'CVO ;return #1 where #3 is  not 'APG ;return #1 of both #4 and #5
['select', 'project', 'project', 'comparative', 'comparative', 'intersection']