We doubt that Bernhard is a frog. It is certain that Greg is a swan. It is highly likely that Mary left the milk. It is highly unlikely that if 'Mary left the milk and Greg is a swan' then Brian is a rhino. There is almost no chance that if either 'Bernhard is a frog' or 'Mary left the milk' but not both then Lily is green. There is almost no chance that if either 'Greg is a swan' or 'Bernhard is a frog' but not both then John discarded the apple.
There is almost no chance that 'Greg is a swan and Lily is green'.
There is almost no chance that 'Greg is a swan and Lily is green'.
There is a better than even chance that 'Greg is a swan and Lily is green'.

  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.
  1.0::factB.
  0.9::factC.
  %hop1
  0.05::factX:-and(factC,factB).
  0.02::factY:-xor(factA,factC).
  0.02::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Greg is a swan and Lily is green'.