There is little chance that Julius is yellow. It is unlikely that Greg is white. There is almost no chance that Brian is a swan. We doubt that if either 'Greg is white' or 'Brian is a swan' but not both then Emily is a sheep. Chances are about even that if 'Brian is a swan and Greg is white' then Mary dropped the milk. It is improbable that if 'Brian is a swan' or 'Julius is yellow' or both then John grabbed the apple.
We believe that 'John grabbed the apple and Emily is a sheep'.
It is impossible that 'John grabbed the apple and Emily is a sheep'.
We believe that 'John grabbed the apple and Emily is a sheep'.

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

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

  query(conclusion).
  
'John grabbed the apple and Emily is a sheep'.