We believe that Julius is a swan. It is highly unlikely that John picked up the apple. We doubt that Daniel left the milk. It is highly likely that if 'Julius is a swan and Daniel left the milk' then Lily is a frog. It is probably the case that if either 'Daniel left the milk' or 'Julius is a swan' but not both then Greg is a lion. There is almost no chance that if 'Julius is a swan and Daniel left the milk' then Mary went to the bedroom.
It is impossible that 'Julius is a swan and Greg is a lion'.
Chances are about even that 'Julius is a swan and Greg is a lion'.
It is impossible that 'Julius is a swan and Greg is a lion'.

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

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

  query(conclusion).
  
'Julius is a swan and Greg is a lion'.