It is unlikely that Greg is gray. It is probably not the case that Winona is a sheep. It is impossible that Lily is a swan. It is highly unlikely that if either 'Greg is gray' or 'Lily is a swan' but not both then Fred dropped the milk. It is probable that if either 'Greg is gray' or 'Winona is a sheep' but not both then Julius is white. Chances are about even that if 'Greg is gray and Lily is a swan' then Brian is a lion.
It is impossible that 'Brian is a lion and Lily is a swan'.
It is impossible that 'Brian is a lion and Lily is a swan'.
There is a better than even chance that 'Brian is a lion and Lily 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
  0.2::factA.
  0.25::factB.
  0.0::factC.
  %hop1
  0.05::factX:-xor(factA,factC).
  0.7::factY:-xor(factA,factB).
  0.5::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Brian is a lion and Lily is a swan'.