If one set of stairs heads in just one direction.
return sets of stairs ;return directions head in  of #1 ;return number of  #2 for each  #1 ;return #1 where  #3 is equal to  one ;return number of  #4 ;return if  #5 is equal to  one
['select', 'project', 'group', 'comparative', 'aggregate', 'boolean']