Is the gray thing in the front the same material as the gray thing in the back
return things ;return #1 that  are gray ;return #2 in  the   back ;return #2 in  the   front ;return the   material of #3 ;return the   material of #4 ;return is  #5 the   same as #6
['select', 'filter', 'filter', 'filter', 'project', 'project', 'boolean']