It is certain that Bernhard is yellow. It is unlikely that Brian is a frog. We believe that Greg is white. It is probably not the case that if either 'Greg is white' or 'Bernhard is yellow' but not both then Mary got the football. There is a better than even chance that if either 'Greg is white' or 'Bernhard is yellow' but not both then Sandra dropped the milk. It is impossible that if 'Brian is a frog' or 'Greg is white' or both then Julius is a rhino.
We doubt that 'Sandra dropped the milk' or 'Bernhard is yellow' or both.
It is certain that 'Sandra dropped the milk' or 'Bernhard is yellow' or both.
We doubt that 'Sandra dropped the milk' or 'Bernhard is yellow' 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
  1.0::factA.
  0.2::factB.
  0.75::factC.
  %hop1
  0.25::factX:-xor(factC,factA).
  0.6::factY:-xor(factC,factA).
  0.0::factZ:-or(factB,factC).

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

  query(conclusion).
  
'Sandra dropped the milk' or 'Bernhard is yellow' or both.