It is probably the case that Brian is white. It is highly likely that Mary got the milk. We believe that Winona is a mouse. It is probably not the case that if 'Winona is a mouse' or 'Mary got the milk' or both then Greg is a rhino. There is a better than even chance that if 'Winona is a mouse and Brian is white' then Julius is green. Chances are slight that if 'Brian is white' or 'Winona is a mouse' or both then John went to the garden.
We believe that 'Brian is white' or 'Greg is a rhino' or both.
We believe that 'Brian is white' or 'Greg is a rhino' or both.
It is improbable that 'Brian is white' 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.
  0.9::factB.
  0.75::factC.
  %hop1
  0.25::factX:-or(factC,factB).
  0.6::factY:-and(factC,factA).
  0.1::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Brian is white' or 'Greg is a rhino' or both.