There is little chance that Brian is a frog. It is probably the case that Fred dropped the apple. There is a better than even chance that Antoine is hungry. It is certain that if 'Antoine is hungry and Fred dropped the apple' then Greg is a lion. We believe that if 'Fred dropped the apple and Brian is a frog' then Bernhard is a rhino. It is improbable that if 'Fred dropped the apple' or 'Brian is a frog' or both then Julius is green.
It is impossible that either 'Brian is a frog' or 'Greg is a lion' but not both.
Chances are about even that either 'Brian is a frog' or 'Greg is a lion' but not both.
It is impossible that either 'Brian is a frog' or 'Greg is a lion' 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
  0.1::factA.
  0.7::factB.
  0.6::factC.
  %hop1
  1.0::factX:-and(factC,factB).
  0.75::factY:-and(factB,factA).
  0.1::factZ:-or(factB,factA).

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

  query(conclusion).
  
Either 'Brian is a frog' or 'Greg is a lion' but not both.