It is improbable that Bernhard is a swan. It is likely that Mary discarded the milk. We doubt that Jessica is a mouse. There is a very good chance that if 'Mary discarded the milk' or 'Bernhard is a swan' or both then Julius is white. There is little chance that if 'Mary discarded the milk' or 'Jessica is a mouse' or both then Jeff went to the bedroom. There is little chance that if 'Jessica is a mouse' or 'Mary discarded the milk' or both then Greg is yellow.
There is a very good chance that either 'Bernhard is a swan' or 'Jessica is a mouse' but not both.
It is probably not the case that either 'Bernhard is a swan' or 'Jessica is a mouse' but not both.
There is a very good chance that either 'Bernhard is a swan' or 'Jessica is a mouse' 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
  0.1::factA.
  0.7::factB.
  0.2::factC.
  %hop1
  0.8::factX:-or(factB,factA).
  0.1::factY:-or(factB,factC).
  0.1::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Jessica is a mouse' but not both.