It is probable that Julius is a rhino. There is almost no chance that Greg is a swan. It is probably not the case that Brian is white. It is probable that if 'Greg is a swan and Brian is white' then John dropped the milk. It is unlikely that if 'Brian is white' or 'Julius is a rhino' or both then Mary left the football. There is little chance that if 'Brian is white' or 'Julius is a rhino' or both then Bernhard is a lion.
It is unlikely that either 'Mary left the football' or 'Bernhard is a lion' but not both.
It is unlikely that either 'Mary left the football' or 'Bernhard is a lion' but not both.
It is almost certain that either 'Mary left the football' or 'Bernhard is a lion' 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.
  0.02::factB.
  0.25::factC.
  %hop1
  0.7::factX:-and(factB,factC).
  0.2::factY:-or(factC,factA).
  0.1::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Mary left the football' or 'Bernhard is a lion' but not both.