We believe that John went to the hallway. It is unlikely that Brian is white. It is probable that Yann is bored. Chances are about even that if 'Brian is white and John went to the hallway' then Bernhard is yellow. It is highly unlikely that if 'Yann is bored' or 'Brian is white' or both then Daniel left the milk. It is almost certain that if 'Brian is white and Yann is bored' then Greg is a lion.
There is almost no chance that 'John went to the hallway' or 'Greg is a lion' or both.
There is a very good chance that 'John went to the hallway' or 'Greg is a lion' or both.
There is almost no chance that 'John went to the hallway' 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
  0.75::factA.
  0.2::factB.
  0.7::factC.
  %hop1
  0.5::factX:-and(factB,factA).
  0.05::factY:-or(factC,factB).
  0.95::factZ:-and(factB,factC).

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

  query(conclusion).
  
'John went to the hallway' or 'Greg is a lion' or both.