There is a very good chance that Greg is a lion. It is highly unlikely that Bill went to the office. Chances are about even that Fred left the football. Chances are slight that if 'Fred left the football and Greg is a lion' then Bernhard is a swan. Chances are about even that if 'Greg is a lion and Fred left the football' then Julius is gray. It is certain that if 'Greg is a lion and Fred left the football' then Brian is a frog.
There is a very good chance that 'Bernhard is a swan' or 'Greg is a lion' or both.
There is a very good chance that 'Bernhard is a swan' or 'Greg is a lion' or both.
It is unlikely that 'Bernhard is a swan' or 'Greg is a lion' 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
  0.8::factA.
  0.05::factB.
  0.5::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.5::factY:-and(factA,factC).
  1.0::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Bernhard is a swan' or 'Greg is a lion' or both.