There is little chance that Greg is a lion. It is probably not the case that Emily is a wolf. We believe that Fred put down the apple. It is certain that if either 'Greg is a lion' or 'Fred put down the apple' but not both then Bernhard is green. It is improbable that if either 'Greg is a lion' or 'Fred put down the apple' but not both then Jason is bored. It is unlikely that if either 'Greg is a lion' or 'Emily is a wolf' but not both then Brian is a rhino.
There is little chance that 'Brian is a rhino' or 'Jason is bored' or both.
There is little chance that 'Brian is a rhino' or 'Jason is bored' or both.
There is a very good chance that 'Brian is a rhino' or 'Jason is bored' or 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.
  0.25::factB.
  0.75::factC.
  %hop1
  1.0::factX:-xor(factA,factC).
  0.1::factY:-xor(factA,factC).
  0.2::factZ:-xor(factA,factB).

  %hop2
  conclusion:-or(factZ,factY).

  query(conclusion).
  
'Brian is a rhino' or 'Jason is bored' or both.