We doubt that John dropped the apple. We believe that Greg is a lion. It is almost certain that Lily is a lion. It is unlikely that if 'Lily is a lion and John dropped the apple' then Julius is a swan. It is impossible that if 'John dropped the apple and Lily is a lion' then Mary left the football. It is highly unlikely that if either 'Greg is a lion' or 'Lily is a lion' but not both then Brian is yellow.
There is a better than even chance that 'Brian is yellow' or 'Julius is a swan' or both.
It is highly unlikely that 'Brian is yellow' or 'Julius is a swan' or both.
There is a better than even chance that 'Brian is yellow' or 'Julius is a swan' 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
  0.2::factA.
  0.75::factB.
  0.95::factC.
  %hop1
  0.2::factX:-and(factC,factA).
  0.0::factY:-and(factA,factC).
  0.05::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Brian is yellow' or 'Julius is a swan' or both.