If one building has gray stone material, the other does not.
return building ;return stone material ;return #2 that is gray ;return #1 that has #3 ;return #1 besides  #4 ;return the  number of  #4 ;return the  number of  #5 ;return if  #6 is equal to  one ;return if  #7 is equal to  one
['select', 'select', 'filter', 'filter', 'discard', 'aggregate', 'aggregate', 'boolean', 'boolean']