It is certain that Bernhard is a frog. It is probably not the case that John went to the garden. We believe that Julius is a rhino. There is almost no chance that if 'John went to the garden and Julius is a rhino' then Bill left the football. It is highly unlikely that if 'Bernhard is a frog' or 'John went to the garden' or both then Mary dropped the milk. It is highly unlikely that if 'Julius is a rhino and John went to the garden' then Brian is yellow.
We doubt that 'Bernhard is a frog' or 'Bill left the football' or both.
It is certain that 'Bernhard is a frog' or 'Bill left the football' or both.
We doubt that 'Bernhard is a frog' or 'Bill left the football' 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.
  0.25::factB.
  0.75::factC.
  %hop1
  0.02::factX:-and(factB,factC).
  0.05::factY:-or(factA,factB).
  0.05::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Bernhard is a frog' or 'Bill left the football' or both.