Chances are about even that Greg is a rhino. There is little chance that Bernhard is a frog. We doubt that John put down the apple. It is probably not the case that if 'Bernhard is a frog and John put down the apple' then Lily is a lion. It is certain that if 'Bernhard is a frog and John put down the apple' then Julius is gray. It is unlikely that if 'John put down the apple' or 'Greg is a rhino' or both then Mary grabbed the milk.
Chances are about even that either 'Lily is a lion' or 'Greg is a rhino' but not both.
Chances are about even that either 'Lily is a lion' or 'Greg is a rhino' but not both.
It is certain that either 'Lily is a lion' or 'Greg is a rhino' 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.
  0.1::factB.
  0.2::factC.
  %hop1
  0.25::factX:-and(factB,factC).
  1.0::factY:-and(factB,factC).
  0.2::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Lily is a lion' or 'Greg is a rhino' but not both.