question: If the dog on the right is being held by a human, the dog on the left is not.
#1 return dog  
#2 return #1 on the  right 
#3 return #1 on the  left 
#4 return human 
#5 return if  #2 is being held by #4 
#6 return if  #3 is not being held by #4 
#7 return if  both  #5 and #6 are true