We doubt that Winona is a mouse. It is unlikely that John dropped the apple. We doubt that Greg is a rhino. It is highly likely that if 'Greg is a rhino' or 'Winona is a mouse' or both then Sumit is bored. It is likely that if 'Winona is a mouse' or 'John dropped the apple' or both then Bernhard is green. It is likely that if 'John dropped the apple and Greg is a rhino' then Mary took the milk.
We doubt that either 'Mary took the milk' or 'Winona is a mouse' but not both.
We doubt that either 'Mary took the milk' or 'Winona is a mouse' but not both.
We believe that either 'Mary took the milk' or 'Winona is a mouse' but not 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
  0.2::factA.
  0.2::factB.
  0.2::factC.
  %hop1
  0.9::factX:-or(factC,factA).
  0.7::factY:-or(factA,factB).
  0.7::factZ:-and(factB,factC).

  %hop2
  conclusion:-xor(factZ,factA).

  query(conclusion).
  
Either 'Mary took the milk' or 'Winona is a mouse' but not both.