Chances are about even that Greg is white. It is improbable that Gertrude is a cat. It is unlikely that Lily is a frog. It is impossible that if either 'Gertrude is a cat' or 'Lily is a frog' but not both then Bernhard is a lion. It is almost certain that if either 'Lily is a frog' or 'Gertrude is a cat' but not both then Brian is a swan. There is almost no chance that if 'Lily is a frog and Gertrude is a cat' then Mary went to the garden.
It is unlikely that 'Lily is a frog and Brian is a swan'.
It is unlikely that 'Lily is a frog and Brian is a swan'.
It is almost certain that 'Lily is a frog and Brian 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
  0.5::factA.
  0.1::factB.
  0.2::factC.
  %hop1
  0.0::factX:-xor(factB,factC).
  0.95::factY:-xor(factC,factB).
  0.02::factZ:-and(factC,factB).

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

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