It is likely that John went to the hallway. It is probable that Greg is a rhino. We believe that Mary put down the apple. It is probably not the case that if either 'Mary put down the apple' or 'Greg is a rhino' but not both then Bernhard is white. There is little chance that if either 'John went to the hallway' or 'Greg is a rhino' but not both then Brian is a lion. It is unlikely that if 'Greg is a rhino and John went to the hallway' then Lily is a frog.
It is improbable that 'John went to the hallway' or 'Greg is a rhino' or both.
It is highly likely that 'John went to the hallway' or 'Greg is a rhino' or both.
It is improbable that 'John went to the hallway' or 'Greg is a rhino' 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
  0.7::factA.
  0.7::factB.
  0.75::factC.
  %hop1
  0.25::factX:-xor(factC,factB).
  0.1::factY:-xor(factA,factB).
  0.2::factZ:-and(factB,factA).

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

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