It is almost certain that Brian is a rhino. It is unlikely that Fred discarded the apple. It is unlikely that Bernhard is a swan. It is highly unlikely that if 'Brian is a rhino and Fred discarded the apple' then Jessica is a mouse. It is probable that if 'Brian is a rhino and Bernhard is a swan' then Sandra dropped the milk. There is a better than even chance that if 'Fred discarded the apple' or 'Bernhard is a swan' or both then John went to the bedroom.
It is probably not the case that either 'Fred discarded the apple' or 'Bernhard is a swan' but not both.
It is probably not the case that either 'Fred discarded the apple' or 'Bernhard is a swan' but not both.
It is probable that either 'Fred discarded the apple' or 'Bernhard 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
  0.95::factA.
  0.2::factB.
  0.2::factC.
  %hop1
  0.05::factX:-and(factA,factB).
  0.7::factY:-and(factA,factC).
  0.6::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'Fred discarded the apple' or 'Bernhard is a swan' but not both.