If there is a stairway with the rails made of wood, the rails are positioned horizontally
return stairway ;return rails of #1 ;return #1 where  #2 are made of wood ;return #3 where  #2 are positioned horizontally ;return number of  #4 ;return if  #5 is at least one
['select', 'project', 'comparative', 'comparative', 'aggregate', 'boolean']