Find the ship type that are used by both ships with Panama and Malta flags.
return ships ;return flags of  #1 ;return #1 where  #2 is  Panama ;return #1 where  #2 is  Malta ;return #1 of  both #3 and #4 ;return ship type of  #5
['select', 'project', 'comparative', 'comparative', 'intersection', 'project']