We believe that Winona is a cat. It is certain that Brian is white. It is improbable that Mary went to the garden. It is unlikely that if 'Winona is a cat and Mary went to the garden' then Greg is white. It is probably the case that if 'Winona is a cat and Brian is white' then Lily is a rhino. Chances are about even that if 'Brian is white' or 'Winona is a cat' or both then Julius is yellow.
There is almost no chance that 'Julius is yellow' or 'Greg is white' or both.
Chances are about even that 'Julius is yellow' or 'Greg is white' or both.
There is almost no chance that 'Julius is yellow' or 'Greg is white' 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.
  1.0::factB.
  0.1::factC.
  %hop1
  0.2::factX:-and(factA,factC).
  0.7::factY:-and(factA,factB).
  0.5::factZ:-or(factB,factA).

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

  query(conclusion).
  
'Julius is yellow' or 'Greg is white' or both.