What are the names of all airports whose elevation is between -50 and 50?
return airports ;return elevations of  #1 ;return #1 where #2 is  at least -50 ;return #1 where #2 is  at most 50 ;return #1 of  both #3 and  #4 ;return names of  #5
['select', 'project', 'comparative', 'comparative', 'intersection', 'project']