It is probable that Julius is a lion. There is little chance that Greg is gray. There is a very good chance that Mary dropped the apple. It is certain that if 'Mary dropped the apple and Julius is a lion' then Bernhard is a rhino. It is highly likely that if 'Julius is a lion and Greg is gray' then John went to the kitchen. It is unlikely that if 'Julius is a lion and Greg is gray' then Jessica is a cat.
Chances are slight that either 'Jessica is a cat' or 'Greg is gray' but not both.
Chances are slight that either 'Jessica is a cat' or 'Greg is gray' but not both.
It is almost certain that either 'Jessica is a cat' or 'Greg is gray' 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.
  0.1::factB.
  0.8::factC.
  %hop1
  1.0::factX:-and(factC,factA).
  0.9::factY:-and(factA,factB).
  0.2::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Jessica is a cat' or 'Greg is gray' but not both.