There is little chance that Mary picked up the milk. There is little chance that Sandra took the apple. It is highly likely that Lily is a swan. It is certain that if either 'Lily is a swan' or 'Mary picked up the milk' but not both then John dropped the milk. It is probably not the case that if either 'Sandra took the apple' or 'Lily is a swan' but not both then Bernhard is yellow. It is probably not the case that if 'Lily is a swan' or 'Mary picked up the milk' or both then Brian is white.
It is highly likely that 'Lily is a swan' or 'Mary picked up the milk' or both.
It is highly likely that 'Lily is a swan' or 'Mary picked up the milk' or both.
Chances are slight that 'Lily is a swan' or 'Mary picked up the milk' 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.
  0.1::factB.
  0.9::factC.
  %hop1
  1.0::factX:-xor(factC,factA).
  0.25::factY:-xor(factB,factC).
  0.25::factZ:-or(factC,factA).

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

  query(conclusion).
  
'Lily is a swan' or 'Mary picked up the milk' or both.