It is certain that Julius is gray. It is probable that Sandra left the football. We believe that Bernhard is a frog. There is little chance that if 'Bernhard is a frog and Julius is gray' then Brian is green. It is highly likely that if 'Julius is gray and Bernhard is a frog' then Jessica is a cat. There is almost no chance that if 'Sandra left the football' or 'Bernhard is a frog' or both then Fred went to the office.
It is highly unlikely that 'Sandra left the football' or 'Julius is gray' or both.
It is certain that 'Sandra left the football' or 'Julius is gray' or both.
It is highly unlikely that 'Sandra left the football' or 'Julius is gray' 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.
  0.7::factB.
  0.75::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.9::factY:-and(factA,factC).
  0.02::factZ:-or(factB,factC).

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

  query(conclusion).
  
'Sandra left the football' or 'Julius is gray' or both.