We believe that Greg is a swan. It is almost certain that Bill went to the kitchen. It is improbable that John took the apple. There is a better than even chance that if 'Bill went to the kitchen' or 'John took the apple' or both then Jessica is a mouse. There is little chance that if either 'Greg is a swan' or 'Bill went to the kitchen' but not both then Julius is a lion. There is almost no chance that if 'Bill went to the kitchen and John took the apple' then Brian is a frog.
Chances are about even that either 'Bill went to the kitchen' or 'Brian is a frog' but not both.
It is almost certain that either 'Bill went to the kitchen' or 'Brian is a frog' but not both.
Chances are about even that either 'Bill went to the kitchen' or 'Brian is a frog' 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.
  0.1::factC.
  %hop1
  0.6::factX:-or(factB,factC).
  0.1::factY:-xor(factA,factB).
  0.02::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Bill went to the kitchen' or 'Brian is a frog' but not both.