There is a very good chance that Greg is a lion. It is highly unlikely that Sandra left the football. Chances are slight that Yann is thirsty. It is improbable that if 'Sandra left the football and Greg is a lion' then Bernhard is gray. There is little chance that if 'Greg is a lion' or 'Yann is thirsty' or both then Daniel dropped the milk. We believe that if 'Greg is a lion and Sandra left the football' then John went to the garden.
There is a very good chance that 'Daniel dropped the milk' or 'Yann is thirsty' or both.
It is unlikely that 'Daniel dropped the milk' or 'Yann is thirsty' or both.
There is a very good chance that 'Daniel dropped the milk' or 'Yann is thirsty' 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.
  0.1::factC.
  %hop1
  0.1::factX:-and(factB,factA).
  0.1::factY:-or(factA,factC).
  0.75::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Daniel dropped the milk' or 'Yann is thirsty' or both.