It is likely that Brian is white. It is highly likely that John dropped the apple. It is probably not the case that Julius is a lion. It is probably not the case that if either 'Brian is white' or 'Julius is a lion' but not both then Gertrude is a sheep. There is little chance that if 'Julius is a lion' or 'Brian is white' or both then Mary left the football. There is a better than even chance that if 'Brian is white' or 'Julius is a lion' or both then Emily is a wolf.
It is probably the case that either 'Mary left the football' or 'Gertrude is a sheep' but not both.
It is unlikely that either 'Mary left the football' or 'Gertrude is a sheep' but not both.
It is probably the case that either 'Mary left the football' 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
  0.7::factA.
  0.9::factB.
  0.25::factC.
  %hop1
  0.25::factX:-xor(factA,factC).
  0.1::factY:-or(factC,factA).
  0.6::factZ:-or(factA,factC).

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

  query(conclusion).
  
Either 'Mary left the football' or 'Gertrude is a sheep' but not both.