It is probably not the case that Sandra took the football. Chances are about even that Brian is a lion. Chances are slight that Gertrude is a sheep. There is a very good chance that if 'Brian is a lion' or 'Sandra took the football' or both then Julius is yellow. It is improbable that if either 'Brian is a lion' or 'Sandra took the football' but not both then Greg is white. It is probably the case that if 'Gertrude is a sheep' or 'Brian is a lion' or both then Mary dropped the apple.
It is highly unlikely that either 'Brian is a lion' or 'Gertrude is a sheep' but not both.
Chances are about even that either 'Brian is a lion' or 'Gertrude is a sheep' but not both.
It is highly unlikely that either 'Brian is a lion' or 'Gertrude is a sheep' 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
  0.25::factA.
  0.5::factB.
  0.1::factC.
  %hop1
  0.8::factX:-or(factB,factA).
  0.1::factY:-xor(factB,factA).
  0.7::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Brian is a lion' or 'Gertrude is a sheep' but not both.