Chances are about even that Julius is a rhino. Chances are about even that Jessica is a cat. There is a very good chance that Greg is a swan. It is certain that if 'Greg is a swan' or 'Julius is a rhino' or both then Bernhard is yellow. It is probable that if 'Greg is a swan' or 'Julius is a rhino' or both then Sandra dropped the milk. There is almost no chance that if 'Greg is a swan and Julius is a rhino' then Mary went to the hallway.
Chances are about even that either 'Julius is a rhino' or 'Mary went to the hallway' but not both.
Chances are about even that either 'Julius is a rhino' or 'Mary went to the hallway' but not both.
It is highly unlikely that either 'Julius is a rhino' or 'Mary went to the hallway' 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
  0.5::factA.
  0.5::factB.
  0.8::factC.
  %hop1
  1.0::factX:-or(factC,factA).
  0.7::factY:-or(factC,factA).
  0.02::factZ:-and(factC,factA).

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

  query(conclusion).
  
Either 'Julius is a rhino' or 'Mary went to the hallway' but not both.