There is almost no chance that Bernhard is a swan. It is highly unlikely that Sandra left the milk. It is certain that Brian is gray. It is probably not the case that if 'Brian is gray and Bernhard is a swan' then Winona is a wolf. There is a very good chance that if 'Brian is gray and Bernhard is a swan' then Greg is a rhino. There is little chance that if either 'Bernhard is a swan' or 'Sandra left the milk' but not both then Julius is yellow.
It is highly unlikely that either 'Sandra left the milk' or 'Winona is a wolf' but not both.
It is highly unlikely that either 'Sandra left the milk' or 'Winona is a wolf' but not both.
It is likely that either 'Sandra left the milk' or 'Winona is a wolf' 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
  0.02::factA.
  0.05::factB.
  1.0::factC.
  %hop1
  0.25::factX:-and(factC,factA).
  0.8::factY:-and(factC,factA).
  0.1::factZ:-xor(factA,factB).

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

  query(conclusion).
  
Either 'Sandra left the milk' or 'Winona is a wolf' but not both.