There is little chance that Lily is yellow. Chances are about even that Gertrude is a sheep. There is almost no chance that Brian is white. There is almost no chance that if 'Gertrude is a sheep' or 'Lily is yellow' or both then Bill left the milk. Chances are slight that if either 'Brian is white' or 'Gertrude is a sheep' but not both then Bernhard is yellow. Chances are about even that if 'Gertrude is a sheep and Brian is white' then Greg is a rhino.
It is highly unlikely that 'Bill left the milk' or 'Gertrude is a sheep' or both.
Chances are about even that 'Bill left the milk' or 'Gertrude is a sheep' or both.
It is highly unlikely that 'Bill left the milk' or 'Gertrude is a sheep' 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.
  0.5::factB.
  0.02::factC.
  %hop1
  0.02::factX:-or(factB,factA).
  0.1::factY:-xor(factC,factB).
  0.5::factZ:-and(factB,factC).

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

  query(conclusion).
  
'Bill left the milk' or 'Gertrude is a sheep' or both.