Chances are slight that Mary went to the hallway. Chances are about even that Greg is a rhino. We believe that Emily is a cat. Chances are slight that if either 'Mary went to the hallway' or 'Greg is a rhino' but not both then Lily is a swan. There is a better than even chance that if either 'Greg is a rhino' or 'Emily is a cat' but not both then Fred is in the school. We believe that if 'Greg is a rhino and Mary went to the hallway' then Bernhard is green.
It is highly unlikely that 'Greg is a rhino' or 'Mary went to the hallway' or both.
There is a better than even chance that 'Greg is a rhino' or 'Mary went to the hallway' or both.
It is highly unlikely that 'Greg is a rhino' or 'Mary went to the hallway' 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
  0.1::factA.
  0.5::factB.
  0.75::factC.
  %hop1
  0.1::factX:-xor(factA,factB).
  0.6::factY:-xor(factB,factC).
  0.75::factZ:-and(factB,factA).

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

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