If the dog on the right is being held by a human, the dog on the left is not.
return dog  ;return #1 on the  right ;return #1 on the  left ;return human ;return if  #2 is being held by #4 ;return if  #3 is not being held by #4 ;return if  both  #5 and #6 are true
['select', 'filter', 'filter', 'select', 'boolean', 'boolean', 'boolean']