It is certain that Julius is a frog. It is improbable that Bernhard is gray. We believe that Greg is a swan. It is highly unlikely that if 'Bernhard is gray and Greg is a swan' then Lily is a frog. We doubt that if 'Greg is a swan and Bernhard is gray' then Fred left the football. There is a better than even chance that if either 'Bernhard is gray' or 'Julius is a frog' but not both then John took the apple.
There is almost no chance that 'Fred left the football' or 'Greg is a swan' or both.
We believe that 'Fred left the football' or 'Greg is a swan' or both.
There is almost no chance that 'Fred left the football' or 'Greg 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
  1.0::factA.
  0.1::factB.
  0.75::factC.
  %hop1
  0.05::factX:-and(factB,factC).
  0.2::factY:-and(factC,factB).
  0.6::factZ:-xor(factB,factA).

  %hop2
  conclusion:-or(factY,factC).

  query(conclusion).
  
'Fred left the football' or 'Greg is a swan' or both.