Find the name of airports whose altitude is between -50 and 50.
return airports ;return altitudes of #1 ;return #1 where #2 is at least -50 ;return #1 where #2 is at most 50 ;return #1 in  both #3 and  #4 ;return names of #5
['select', 'project', 'comparative', 'comparative', 'intersection', 'project']