We doubt that Lily is green. It is probably not the case that Julius is a swan. It is probably the case that Mary dropped the milk. It is probable that if 'Mary dropped the milk' or 'Julius is a swan' or both then Greg is white. It is impossible that if 'Lily is green and Mary dropped the milk' then Bernhard is a lion. Chances are about even that if 'Julius is a swan' or 'Mary dropped the milk' or both then Brian is green.
It is likely that 'Brian is green and Julius is a swan'.
Chances are slight that 'Brian is green and Julius is a swan'.
It is likely that 'Brian is green and Julius 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.
  0.7::factC.
  %hop1
  0.7::factX:-or(factC,factB).
  0.0::factY:-and(factA,factC).
  0.5::factZ:-or(factB,factC).

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

  query(conclusion).
  
'Brian is green and Julius is a swan'.