It is unlikely that Bernhard is a rhino. There is a better than even chance that Greg is a swan. It is likely that Mary dropped the milk. There is a very good chance that if 'Bernhard is a rhino' or 'Greg is a swan' or both then Sumit is thirsty. Chances are slight that if 'Bernhard is a rhino' or 'Mary dropped the milk' or both then Fred went to the garden. There is almost no chance that if 'Greg is a swan' or 'Bernhard is a rhino' or both then Emily is a cat.
It is probable that either 'Sumit is thirsty' or 'Greg is a swan' but not both.
We doubt that either 'Sumit is thirsty' or 'Greg is a swan' but not both.
It is probable that either 'Sumit is thirsty' or 'Greg is a swan' but not both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.2::factA.
  0.6::factB.
  0.7::factC.
  %hop1
  0.8::factX:-or(factA,factB).
  0.1::factY:-or(factA,factC).
  0.02::factZ:-or(factB,factA).

  %hop2
  conclusion:-xor(factX,factB).

  query(conclusion).
  
Either 'Sumit is thirsty' or 'Greg is a swan' but not both.