There is little chance that Bernhard is gray. It is likely that Greg is a swan. It is impossible that Lily is a lion. We believe that if 'Lily is a lion and Greg is a swan' then John dropped the apple. There is a very good chance that if either 'Lily is a lion' or 'Bernhard is gray' but not both then Julius is white. Chances are slight that if 'Greg is a swan and Bernhard is gray' then Sandra took the milk.
It is impossible that 'Sandra took the milk' or 'Lily is a lion' or both.
It is impossible that 'Sandra took the milk' or 'Lily is a lion' or both.
It is certain that 'Sandra took the milk' or 'Lily is a lion' 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.
  0.7::factB.
  0.0::factC.
  %hop1
  0.75::factX:-and(factC,factB).
  0.8::factY:-xor(factC,factA).
  0.1::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Sandra took the milk' or 'Lily is a lion' or both.