There is a better than even chance that Fred dropped the milk. It is highly unlikely that Lily is a rhino. It is improbable that Bernhard is a swan. It is probably the case that if 'Bernhard is a swan and Lily is a rhino' then Brian is a frog. It is highly unlikely that if 'Lily is a rhino and Bernhard is a swan' then Julius is a lion. We doubt that if 'Bernhard is a swan' or 'Lily is a rhino' or both then Mary left the apple.
It is highly unlikely that either 'Lily is a rhino' or 'Brian is a frog' but not both.
It is highly unlikely that either 'Lily is a rhino' or 'Brian is a frog' but not both.
It is probably the case that either 'Lily is a rhino' or 'Brian is a frog' 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
  0.6::factA.
  0.05::factB.
  0.1::factC.
  %hop1
  0.7::factX:-and(factC,factB).
  0.05::factY:-and(factB,factC).
  0.2::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Lily is a rhino' or 'Brian is a frog' but not both.