Chances are about even that John put down the apple. It is probably not the case that Greg is a frog. It is probable that Brian is a swan. Chances are about even that if 'Greg is a frog' or 'Brian is a swan' or both then Jessica is a cat. We believe that if 'Greg is a frog' or 'Brian is a swan' or both then Fred is in the school. Chances are slight that if 'Greg is a frog' or 'Brian is a swan' or both then Mary dropped the milk.
There is almost no chance that either 'John put down the apple' or 'Jessica is a cat' but not both.
Chances are about even that either 'John put down the apple' or 'Jessica is a cat' but not both.
There is almost no chance that either 'John put down the apple' or 'Jessica is a cat' 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
  0.5::factA.
  0.25::factB.
  0.7::factC.
  %hop1
  0.5::factX:-or(factB,factC).
  0.75::factY:-or(factB,factC).
  0.1::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'John put down the apple' or 'Jessica is a cat' but not both.