It is certain that Bill left the football. Chances are slight that Greg is a lion. It is almost certain that Mary went to the office. We doubt that if either 'Bill left the football' or 'Greg is a lion' but not both then Brian is a rhino. There is almost no chance that if either 'Bill left the football' or 'Mary went to the office' but not both then Lily is a swan. There is almost no chance that if 'Greg is a lion and Bill left the football' then Bernhard is yellow.
It is highly likely that either 'Greg is a lion' or 'Lily is a swan' but not both.
There is little chance that either 'Greg is a lion' or 'Lily is a swan' but not both.
It is highly likely that either 'Greg is a lion' or 'Lily is a swan' 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
  1.0::factA.
  0.1::factB.
  0.95::factC.
  %hop1
  0.2::factX:-xor(factA,factB).
  0.02::factY:-xor(factA,factC).
  0.02::factZ:-and(factB,factA).

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

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