It is probably the case that Gertrude is a sheep. There is a very good chance that Greg is a swan. It is certain that John went to the office. Chances are about even that if 'Greg is a swan' or 'Gertrude is a sheep' or both then Bernhard is a swan. There is a better than even chance that if 'Greg is a swan' or 'Gertrude is a sheep' or both then Mary is in the bathroom. It is likely that if either 'Greg is a swan' or 'John went to the office' but not both then Sumit is tired.
Chances are about even that either 'Bernhard is a swan' or 'Mary is in the bathroom' but not both.
Chances are about even that either 'Bernhard is a swan' or 'Mary is in the bathroom' but not both.
There is almost no chance that either 'Bernhard is a swan' or 'Mary is in the bathroom' 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
  0.7::factA.
  0.8::factB.
  1.0::factC.
  %hop1
  0.5::factX:-or(factB,factA).
  0.6::factY:-or(factB,factA).
  0.7::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Mary is in the bathroom' but not both.