It is probably not the case that John left the football. It is highly unlikely that Sandra dropped the milk. It is certain that Greg is a rhino. It is almost certain that if either 'Sandra dropped the milk' or 'John left the football' but not both then Lily is a rhino. Chances are slight that if 'Sandra dropped the milk' or 'Greg is a rhino' or both then Brian is yellow. We doubt that if 'John left the football and Greg is a rhino' then Mary went to the kitchen.
It is probably not the case that 'Brian is yellow' or 'Greg is a rhino' or both.
It is certain that 'Brian is yellow' or 'Greg is a rhino' or both.
It is probably not the case that 'Brian is yellow' 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
  0.25::factA.
  0.05::factB.
  1.0::factC.
  %hop1
  0.95::factX:-xor(factB,factA).
  0.1::factY:-or(factB,factC).
  0.2::factZ:-and(factA,factC).

  %hop2
  conclusion:-or(factY,factC).

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