It is improbable that Winona is a wolf. There is almost no chance that Julius is a rhino. It is likely that Fred is in the school. It is certain that if either 'Fred is in the school' or 'Julius is a rhino' but not both then Bernhard is a swan. It is impossible that if 'Winona is a wolf and Julius is a rhino' then Brian is white. Chances are about even that if 'Winona is a wolf and Fred is in the school' then Mary dropped the milk.
It is impossible that 'Brian is white and Bernhard is a swan'.
It is impossible that 'Brian is white and Bernhard is a swan'.
We believe that 'Brian is white and Bernhard is a swan'.

  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.
  0.02::factB.
  0.7::factC.
  %hop1
  1.0::factX:-xor(factC,factB).
  0.0::factY:-and(factA,factB).
  0.5::factZ:-and(factA,factC).

  %hop2
  conclusion:-and(factY,factX).

  query(conclusion).
  
'Brian is white and Bernhard is a swan'.