It is improbable that Mary left the football. There is a very good chance that Julius is yellow. It is highly unlikely that Brian is a lion. It is certain that if 'Julius is yellow' or 'Mary left the football' or both then Greg is a swan. We doubt that if 'Mary left the football' or 'Julius is yellow' or both then Emily is a mouse. It is impossible that if 'Brian is a lion' or 'Julius is yellow' or both then John grabbed the apple.
There is little chance that 'Julius is yellow' or 'John grabbed the apple' or both.
There is a very good chance that 'Julius is yellow' or 'John grabbed the apple' or both.
There is little chance that 'Julius is yellow' or 'John grabbed the apple' 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.
  0.8::factB.
  0.05::factC.
  %hop1
  1.0::factX:-or(factB,factA).
  0.2::factY:-or(factA,factB).
  0.0::factZ:-or(factC,factB).

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

  query(conclusion).
  
'Julius is yellow' or 'John grabbed the apple' or both.