There is almost no chance that Yann is hungry. Chances are about even that Jeff dropped the apple. We doubt that Greg is a swan. It is unlikely that if 'Jeff dropped the apple' or 'Greg is a swan' or both then Julius is a swan. It is likely that if either 'Greg is a swan' or 'Jeff dropped the apple' but not both then Mary went to the garden. It is impossible that if 'Greg is a swan and Yann is hungry' then Lily is green.
It is impossible that 'Greg is a swan and Yann is hungry'.
It is impossible that 'Greg is a swan and Yann is hungry'.
Chances are about even that 'Greg is a swan and Yann is hungry'.

  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
  0.02::factA.
  0.5::factB.
  0.2::factC.
  %hop1
  0.2::factX:-or(factB,factC).
  0.7::factY:-xor(factC,factB).
  0.0::factZ:-and(factC,factA).

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

  query(conclusion).
  
'Greg is a swan and Yann is hungry'.