We believe that Greg is a lion. It is almost certain that John took the apple. It is likely that Mary went to the kitchen. It is highly likely that if either 'John took the apple' or 'Greg is a lion' but not both then Emily is a wolf. It is almost certain that if either 'John took the apple' or 'Greg is a lion' but not both then Julius is a swan. There is a better than even chance that if 'Mary went to the kitchen' or 'Greg is a lion' or both then Lily is white.
We believe that either 'Julius is a swan' or 'John took the apple' but not both.
We believe that either 'Julius is a swan' or 'John took the apple' but not both.
There is little chance that either 'Julius is a swan' or 'John took the apple' 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
  0.75::factA.
  0.95::factB.
  0.7::factC.
  %hop1
  0.9::factX:-xor(factB,factA).
  0.95::factY:-xor(factB,factA).
  0.6::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Julius is a swan' or 'John took the apple' but not both.