Chances are slight that Julius is a swan. It is probably not the case that Bernhard is a frog. There is a very good chance that Sandra took the milk. It is highly unlikely that if either 'Sandra took the milk' or 'Bernhard is a frog' but not both then Lily is green. It is certain that if 'Bernhard is a frog and Sandra took the milk' then Greg is a lion. There is a better than even chance that if either 'Julius is a swan' or 'Sandra took the milk' but not both then Fred is in the cinema.
There is a better than even chance that either 'Greg is a lion' or 'Sandra took the milk' but not both.
There is a better than even chance that either 'Greg is a lion' or 'Sandra took the milk' but not both.
It is highly unlikely that either 'Greg is a lion' or 'Sandra took the milk' 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.
  0.25::factB.
  0.8::factC.
  %hop1
  0.05::factX:-xor(factC,factB).
  1.0::factY:-and(factB,factC).
  0.6::factZ:-xor(factA,factC).

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

  query(conclusion).
  
Either 'Greg is a lion' or 'Sandra took the milk' but not both.