We doubt that Brian is a rhino. It is certain that Daniel dropped the apple. There is little chance that Bernhard is a lion. It is highly unlikely that if 'Bernhard is a lion and Daniel dropped the apple' then Julius is a swan. Chances are slight that if 'Daniel dropped the apple and Brian is a rhino' then Emily is a wolf. It is probably the case that if either 'Bernhard is a lion' or 'Brian is a rhino' but not both then Greg is white.
We believe that either 'Julius is a swan' or 'Bernhard is a lion' but not both.
Chances are slight that either 'Julius is a swan' or 'Bernhard is a lion' but not both.
We believe that either 'Julius is a swan' or 'Bernhard 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
  0.2::factA.
  1.0::factB.
  0.1::factC.
  %hop1
  0.05::factX:-and(factC,factB).
  0.1::factY:-and(factB,factA).
  0.7::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Julius is a swan' or 'Bernhard is a lion' but not both.