It is certain that Bernhard is a swan. We doubt that Brian is yellow. It is probable that John left the milk. It is almost certain that if 'John left the milk' or 'Bernhard is a swan' or both then Gertrude is a cat. We believe that if 'Bernhard is a swan and Brian is yellow' then Jessica is a mouse. We doubt that if 'Brian is yellow' or 'Bernhard is a swan' or both then Julius is gray.
It is likely that 'Bernhard is a swan and John left the milk'.
It is likely that 'Bernhard is a swan and John left the milk'.
It is impossible that 'Bernhard is a swan and John left the milk'.

  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
  1.0::factA.
  0.2::factB.
  0.7::factC.
  %hop1
  0.95::factX:-or(factC,factA).
  0.75::factY:-and(factA,factB).
  0.2::factZ:-or(factB,factA).

  %hop2
  conclusion:-and(factA,factC).

  query(conclusion).
  
'Bernhard is a swan and John left the milk'.