It is highly unlikely that Sandra dropped the milk. It is certain that Brian is gray. It is highly unlikely that Julius is a frog. It is unlikely that if 'Sandra dropped the milk and Brian is gray' then Lily is a swan. It is probably not the case that if 'Brian is gray and Sandra dropped the milk' then Winona is a wolf. It is unlikely that if 'Sandra dropped the milk and Julius is a frog' then Fred went to the garden.
We believe that 'Lily is a swan and Brian is gray'.
There is almost no chance that 'Lily is a swan and Brian is gray'.
We believe that 'Lily is a swan and Brian is gray'.

  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
  0.05::factA.
  1.0::factB.
  0.05::factC.
  %hop1
  0.2::factX:-and(factA,factB).
  0.25::factY:-and(factB,factA).
  0.2::factZ:-and(factA,factC).

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

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